Method for selecting, in selection period, subframe excluding subframe relating to subframe in which transmission has been performed during sensing period in wireless communication system, and terminal using same

ABSTRACT

The present invention provides a vehicle-to-X (V2X) operation method performed by a V2X terminal in a wireless communication system, the method comprising: selecting, in a selection period, a subframe excluding a subframe relating to a subframe in which transmission has been performed during a sensing period; and performing a V2X communication on the basis of the selected subframe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Application No. 17/235,073,filed on Apr. 20, 2021, which is a continuation of U.S. Application No16/809,982, filed on Mar. 5, 2020, now U.S. Pat. No. 10,993,095, whichis a continuation of U.S. Application No. 16/314,954, filed on Jan. 3,2019, now U.S. Pat. No. 10,993,092, which is a National Stage filingunder 35 U.S.C. 371 of International Application No. PCT/KR2017/003844,filed on Apr. 7, 2017, which claims the benefit of U.S. ProvisionalApplications No. 62/385,962 filed on Sep. 10, 2016, No. 62/385,967 filedon Sep. 10, 2016, No. 62/393,158 filed on Sep. 12, 2016, No. 62/400,620filed on Sep. 27, 2016, No. 62/400,683 filed on Sep. 28, 2016, No.62/401,188 filed on Sep. 29, 2016, No. 62/403,048 filed on Sep. 30,2016, No. 62/403,673 filed on Oct. 3, 2016, No. 62/406,373 filed on Oct.10, 2016, No. 62/406,468 filed on Oct. 11, 2016, and No. 62/421,401filed on Nov. 14, 2016. The disclosures of the prior applications areincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communication and, moreparticularly, to a method for selecting V2X transmission resourcesperformed by a terminal in a wireless communication system and aterminal using the method.

Related Art

The International Telecommunication Union Radio communication sector(ITU-R) is conducting standardization of the International MobileTelecommunications (IMT)-Advanced which is the next-generation mobilecommunication system following the 3rd generation mobile communicationsystem. IMT-Advanced aims to support Internet Protocol (IP)-basedmultimedia services with a data rate of 1 Gbps while a terminal is atfixed positions or moves at low speeds and with a data rate of 100 Mbpswhile a terminal moves at high speeds.

The 3rd Generation Partnership Project (3GPP) is developing LTE-A, whichis an advanced version of the Long Term Evolution (LTE) based onOrthogonal Frequency Division Multiple Access (OFDMA)/SingleCarrier-Frequency Division Multiple Access (SC-FDMA) transmissionscheme, as a system standard to satisfy the requirements of theIMT-Advanced. The LTE-A is one of strong candidates for theIMT-Advanced.

Recently, there has been a growing interest in the Device-to-Device(D2D) technology which enables direct communication between devices. Inparticular, D2D communication is getting attention as a communicationtechnology to implement a public safety network. Although commercialcommunication networks are changing fast to adopt the LTE standard, thecurrent public safety network is still relying on the 2G technologybecause of collision problems with existing communication standards andcost issues. Such technology gap and the demand for improved serviceshave led to the efforts to improve public safety networks.

The D2D communication may be extended to be used for signal transmissionand reception between vehicles, where vehicle-related communication isparticularly called Vehicle-to-Everything (V2X) communication. The ‘X’in the V2X represents pedestrian (communication between a vehicle and adevice carried by individual (for example, handheld terminal carried bya pedestrian, cyclist, driver, or passenger), where, in this case, V2Xmay be expressed by V2P), vehicle (communication between vehicles, V2V),infrastructure/network (communication between a vehicle and a roadsideunit (RSU)/network, where RSU is a transportation infrastructure entity,for example, an entity transmitting speed notifications implemented inan eNB or a stationary UE, V2I/N). A (V2P communication-related) devicecarried by a pedestrian (or person) is called a “P-UE” while a (V2Xcommunication-related) device installed in a vehicle is called a “V-UE”.The term ‘entity’ in this document may be interpreted as P-UE, V-UE orRSU (/network/i nfrastructure).

Meanwhile, in V2X communication, it may be problematic to select whichresource in which way when a P-UE tries to transmit a V2X signal P-UEstend to be sensitive to battery consumption unlike vehicle-mountedterminals. Also, in V2X communication, it may be important to transmit asignal periodically and not to exert interference on other terminals. Amethod for selecting a transmission resource for a P-UE needs to bedetermined by taking into account the facts above.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for selectinga V2X transmission resource performed by a UE in a wirelesscommunication system and a UE using the method.

In an aspect, a method for performing a vehicle-to-X (V2X) operation ina wireless communication system is provided. The method may be performedby a V2X user equipment (UE) and comprise selecting a subframe excludinga subframe related to a subframe on which a transmission is performedwithin a sensing duration, within a selection duration and performing aV2X communication based on the selected subframe.

The excluded subframe may be a subframe within the selection duration.

When a subframe corresponding the subframe on which the transmission isperformed within the sensing duration based on a specific periodoverlaps a subframe reserved according to a resource reservation periodof the related subframe, the related subframe may be excluded.

The subframe on which the transmission may be performed is a subframe k,and the k is a positive integer, the subframe corresponding the subframek based on the specific period may be a subframe (k+100*i), and the imay be a positive integer configured by a base station, and if thesubframe (k+100*i) overlaps a subframe (y+P*j), the subframe y may beexcluded, and the y may be positive integer, the P may be the resourcereservation period and the j may be a positive integer.

A range of the j may be determined based on a positive integer valueproportional to a counter value randomly determined by the V2X UE.

The counter value may be same or larger than 5 and same or smaller than15.

The P may be 100 ms.

The sensing period may be 1 s, and the selection duration may be 100 ms.

The sensing duration may be a sensing window and the selection durationis a selection window.

The sensing window may be specific to the V2X UE.

In another aspect, a User Equipment (UE) is provided. The UE may omprisea Radio Frequency (RF) unit transmitting and receiving a radio signaland a processor operating being combined with the RF unit. The processormay be configured to select a subframe excluding a subframe related to asubframe on which a transmission is performed within a sensing duration,within a selection duration, and perform a vehicle-to-X (V2X)communication based on the selected subframe.

According to the present invention, resources involved in V2Xcommunication may be reserved in an efficient manner when a UE performV2X communication. Therefore, since a UE according to the presentinvention makes use of radio resources efficiently, unnecessaryoccupation of radio resources is minimized, and thereby efficiency ofradio resource is maximized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane.

FIG. 3 is a diagram showing a wireless protocol architecture for acontrol plane.

FIG. 4 illustrates a reference structure for a ProSe.

FIG. 5 illustrates arrangement examples of terminals performing ProSedirect communication and cell coverage.

FIG. 6 illustrates a user plane protocol stack for the ProSe directcommunication

FIG. 7 illustrates a PC 5 interface for D2D discovery.

FIG. 8 is a flow diagram illustrating a method for performing V2Xcommunication based on a UE-specific sensing period according to oneembodiment of the present invention.

FIG. 9 illustrates an example of a UE-specific sensing window.

FIG. 10 is a flow diagram illustrating a method for configuring aselection window according to one embodiment of the present invention.

FIGS. 11 and 12 illustrate the proposed rule#1.

FIGS. 13 and 14 illustrate determining a re-reservation (or selection)resource and performing a V2X message immediately by using there-reserved (or selected) resource.

FIGS. 15 and 16 illustrate one example of a case in which (from aviewpoint of a ‘single V2X UE’) ‘control (or scheduling) information’and ‘data (associated with the corresponding control (or scheduling)information)’ are transmitted on the same SF according to the FrequencyDivision Multiplexing (FDM) scheme.

FIG. 17 illustrates one example of a case in which a ‘control (orscheduling) information transmission pool’ and a ‘data transmissionpool’ are defined (or configured) according to the ‘FDM’ scheme (from asystem point of view).

FIG. 18 is a flow diagram illustrating a method for performing sensingwhen multiple sub-channels are used for transmission of a V2X messageaccording to one embodiment of the present invention.

FIG. 19 illustrates one example in which ENERGY MEASUREMENT (namelysensing) is performed with a sub-channel size of data to be transmittedby the UE.

FIGS. 20 and 21 illustrate one example of ‘PARTIALLY OVERLAPPED REGIONBASED SENSING’ (or ‘SLIDING WINDOW BASED SENSING’).

FIG. 22 illustrates a situation in which the “SYSTEM FRAME NUMBER (SFN)WRAP AROUND” problem occurs.

FIG. 23 is a flow diagram illustrating a method for reserving a finitenumber of resources according to one embodiment of the presentinvention.

FIG. 24 is a flow diagram of a method for a UE to reselect a resourceaccording to one embodiment of the present invention.

FIG. 25 illustrates one example of a method for performing resourcereservation by taking into account the proposal described above.

FIG. 26 is a flow diagram of a method for excluding a subframe (from aselection window) related to the subframe in which the UE has failed toperform sensing according to one embodiment of the present invention.

FIG. 27 illustrates an example in which a subframe (from a selectionwindow) related to a subframe in which the UE has failed to performsensing.

FIGS. 28 to 30 illustrate an example reflecting a resource in the“RESOURCE EXCLUSION PROCEDURE (BASED ON PSSCH-RSRP MEASUREMENT.

FIG. 31 illustrates one example of a case in which the (existing) “DFNRANGE” value (for example, “10240” or “10176”) is increased.

FIG. 32 illustrates one example of transmitting updated systeminformation.

FIG. 33 illustrates one example of a hyper DFN.

FIG. 34 is a flow diagram of a method for performing V2X communicationon an allocated V2X resource pool according to one embodiment of thepresent invention.

FIG. 35 illustrates an example in which an SLSS subframe is excludedfrom V2X transmission.

FIG. 36 illustrates an example in which DL and S subframe are excludedfrom V2X transmission.

FIG. 37 is a flow diagram of a method for performing reservation of aV2X transmission resource when resource reservation is set with arelatively short period (for example, 20 ms or 50 ms (shorter than 100ms)) according to one embodiment of the present invention.

FIG. 38 is a flow diagram of a method for performing sensing with arelatively short period when resource reservation with a short period isset according to one embodiment of the present invention.

FIG. 39 is a block diagram of a UE in which an embodiment of the presentinvention is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a wireless communication system to which the presentinvention is applied. The wireless communication system may also bereferred to as an evolved-UMTS terrestrial radio access network(E-UTRAN) or a long term evolution (LTE)/LTE-A system.

The E-UTRAN includes at least one base station (BS) 20 which provides acontrol plane and a user plane to a user equipment (UE) 10. The UE 10may be fixed or mobile, and may be referred to as another terminology,such as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a mobile terminal (MT), a wireless device, etc. The BS 20is generally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC) 30, more specifically, to a mobility management entity (MME)through S1-MME and to a serving gateway (S-GW) through S1-U.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information of the UE or capabilityinformation of the UE, and such information is generally used formobility management of the UE. The S-GW is a gateway having an E-UTRANas an end point. The P-GW is a gateway having a PDN as an end point.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. Among them, a physical (PHY) layer belonging to the first layerprovides an information transfer service by using a physical channel,and a radio resource control (RRC) layer belonging to the third layerserves to control a radio resource between the UE and the network. Forthis, the RRC layer exchanges an RRC message between the UE and the BS.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane. FIG. 3 is a diagram showing a wireless protocol architecture fora control plane. The user plane is a protocol stack for user datatransmission. The control plane is a protocol stack for control signaltransmission.

Referring to FIGS. 2 and 3 , a PHY layer provides an upper layer with aninformation transfer service through a physical channel. The PHY layeris connected to a medium access control (MAC) layer which is an upperlayer of the PHY layer through a transport channel. Data is transferredbetween the MAC layer and the PHY layer through the transport channel.The transport channel is classified according to how and with whatcharacteristics data is transferred through a radio interface.

Data is moved between different PHY layers, that is, the PHY layers of atransmitter and a receiver, through a physical channel. The physicalchannel may be modulated according to an Orthogonal Frequency DivisionMultiplexing (OFDM) scheme, and use the time and frequency as radioresources.

The functions of the MAC layer include mapping between a logical channeland a transport channel and multiplexing and demultiplexing to atransport block that is provided through a physical channel on thetransport channel of a MAC Service Data Unit (SDU) that belongs to alogical channel. The MAC layer provides service to a Radio Link Control(RLC) layer through the logical channel.

The functions of the RLC layer include the concatenation, segmentation,and reassembly of an RLC SDU. In order to guarantee various types ofQuality of Service (QoS) required by a Radio Bearer (RB), the RLC layerprovides three types of operation mode: Transparent Mode (TM),Unacknowledged Mode (UM), and Acknowledged Mode (AM). AM RLC provideserror correction through an Automatic Repeat Request (ARQ).

The RRC layer is defined only on the control plane The RRC layer isrelated to the configuration, reconfiguration, and release of radiobearers, and is responsible for control of logical channels, transportchannels, and PHY channels. An RB means a logical route that is providedby the first layer (PHY layer) and the second layers (MAC layer, the RLClayer, and the PDCP layer) in order to transfer data between UE and anetwork.

The function of a Packet Data Convergence Protocol (PDCP) layer on theuser plane includes the transfer of user data and header compression andciphering. The function of the PDCP layer on the user plane furtherincludes the transfer and encryption/integrity protection of controlplane data.

What an RB is configured means a procedure of defining thecharacteristics of a wireless protocol layer and channels in order toprovide specific service and configuring each detailed parameter andoperating method. An RB can be divided into two types of a Signaling RB(SRB) and a Data RB (DRB). The SRB is used as a passage through which anRRC message is transmitted on the control plane, and the DRB is used asa passage through which user data is transmitted on the user plane

If RRC connection is established between the RRC layer of UE and the RRClayer of an E-UTRAN, the UE is in the RRC connected state. If not, theUE is in the RRC idle state.

A downlink transport channel through which data is transmitted from anetwork to UE includes a broadcast channel (BCH) through which systeminformation is transmitted and a downlink shared channel (SCH) throughwhich user traffic or control messages are transmitted. Traffic or acontrol message for downlink multicast or broadcast service may betransmitted through the downlink SCH, or may be transmitted through anadditional downlink multicast channel (MCH). Meanwhile, an uplinktransport channel through which data is transmitted from UE to a networkincludes a random access channel (RACH) through which an initial controlmessage is transmitted and an uplink shared channel (SCH) through whichuser traffic or control messages are transmitted.

Logical channels that are placed over the transport channel and that aremapped to the transport channel include a broadcast control channel(BCCH), a paging control channel (PCCH), a common control channel(CCCH), a multicast control channel (MCCH), and a multicast trafficchannel (MTCH).

The physical channel includes several OFDM symbols in the time domainand several subcarriers in the frequency domain. One subframe includes aplurality of OFDM symbols in the time domain. An RB is a resourcesallocation unit, and includes a plurality of OFDM symbols and aplurality of subcarriers. Furthermore, each subframe may use specificsubcarriers of specific OFDM symbols (e.g., the first OFDM symbol) ofthe corresponding subframe for a physical downlink control channel(PDCCH), that is, an L1/L2 control channel. A Transmission Time Interval(TTI) is a unit time for subframe transmission.

Hereinafter, a D2D operation will be described. In the 3GPP LTE-A, aservice related to the D2D operation refers to Proximity based Services(ProSe). Hereinafter, the ProSe is an equivalent concept with the D2Doperation and the ProSe may be compatibly used with the D2D operation.The ProSe is now described.

The ProSe includes ProSe direct communication and ProSe directdiscovery. The ProSe direct communication presents communicationperformed by two or more adjacent terminals. The terminals may performcommunication using a protocol of a user plane. A ProSe-enabled UE meansa UE for supporting a process related to requirements of the ProSe.Unless otherwise defined, the ProSe-enabled UE includes both of a publicsafety UE and a non-public safety UE. The public safety UE represents aUE for supporting both of a public safety specified function and theProSe process. The non-public safety UE is a terminal which supports theProSe process but does not support the public safety specified function.

The ProSe direct discovery is a process where the ProSe-enabled UEdiscovers another ProSe-enabled UE. In this case, only ability of thetwo ProSe-enabled UEs is used. An EPC-level ProSe discovery signifies aprocess where an EPC determines whether 2 ProSe enable terminals areclosed to each other, and reports the close state thereof the two ProSeenabled terminals.

Hereinafter, the ProSe direct communication may refer to D2Dcommunication, and the ProSe direct discovery may refer to D2Ddiscovery.

FIG. 4 illustrates a reference structure for a ProSe.

Referring to FIG. 4 , the reference structure for a ProSe includes aplurality of terminals having E-UTRAN, EPC, and ProSe applicationprogram, a ProSe application (APP) server, and a ProSe function.

An EPC is a representative example of the E-UTRAN. The EPC may includean MME, an S-GW, a P-GW, a policy and charging rules function (PCRF),and a home subscriber server (HSS).

The ProSe application server is a user of ProSe in order to make anapplication function. The ProSe application server may communicate withan application program in the terminal. The application program in theterminal may use a ProSe ability to make an application function.

The ProSe function may include at least one of following functions butis not limited thereto.

-   Interworking via a reference point towards the 3rd party    applications-   Authorization and configuration of the UE for discovery and direct    communication)-   Enable the function of the EPC level ProSe discovery-   ProSe related new subscriber data and handling of data storage, and    also handling of ProSe identities-   Security related function-   Provide control towards the EPC for policy related function-   Provide function for charging (via or outside of EPC, e.g., offline    charging))

Hereinafter, a reference point and a reference interface will bedescribed in a reference structure for the ProSe.

-   PC1: a reference point between a ProSe application program in the    terminal and a ProSe application program in a ProSe application    server. The PC1 is used to define signaling requirements in an    application level.-   PC2: is a reference point between the ProSe application server and a    ProSe function. The PC2 is used to define an interaction between the    ProSe application server and a ProSe function. An application data    update of a ProSe database of the ProSe function may be an example    of the interaction.-   PC3: is a reference point between the terminal and the ProSe    function. The PC3 is used to define an interaction between the    terminal and the ProSe function Configuration for ProSe discovery    and communication may be an example of the interaction.-   PC4: is a reference point between an EPC and the ProSe function. The    PC4 is used to define an interaction between the EPC and the ProSe    function. The interaction lay illustrate when a path for 1:1    communication or a ProSe service for real time session management or    mobility management are authorized.-   PC5: is a reference point to use control/user plane for discovery,    communication, and relay between terminals, and 1:1 communication-   PC6: is a reference point to use a function such as ProSe discovery    between users included in different PLMNs.-   SGi: may be used for application data and application level control    information exchange.

ProSe Direct Communication (D2D Communication)

The ProSe direct communication is a communication mode where two publicsafety terminals may perform direct communication through a PC 5interface. The communication mode may be supported in both of a case ofreceiving a service in coverage of E-UTRAN or a case of separating thecoverage of E-UTRAN.

FIG. 5 illustrates arrangement examples of terminals performing ProSedirect communication and cell coverage.

Referring to FIG. 5(a), UEs A and B may be located outside of the cellcoverage. Referring to FIG. 5(b), the UE A may be located in the cellcoverage and the UE B may be located outside of the cell coverage.Referring to FIG. 5(c), both of UEs A and B may be located in the cellcoverage. Referring to FIG. 5(d), the UE A may be located in coverage ofa first cell and the UE B may be in coverage of a second cell.

As described above, the ProSe direct communication may be performedbetween terminals which are provided at various positions.

Meanwhile, following IDs may be used in the ProSe direct communication.

Source layer-2 ID: The source layer-2 ID identifies a sender of a packetin a PC 5 interface.

Purpose layer-2 ID : The purpose layer-2 ID identifies a target of apacket in a PC 5 interface.

SA L1 ID : The SA L1 ID represents an in an ID in a schedulingassignment (SA) in the PC 5 interface.

FIG. 6 illustrates a user plane protocol stack for the ProSe directcommunication.

Referring to FIG. 6 , the PC 5 interface includes a PDCH layer, a RLClayer, a MAC layer, and a PHY layer.

There may not be HARQ feedback in the ProSe direct communication. An MACheader may include the source layer-2 ID and the purpose layer-2 ID.

Radio Resource Assignment for ProSe Direct Communication

A ProSe enable terminal may use following two modes with respect toresource assignments for the ProSe direct communication.

1. Mode 1

The mode 2 is a mode for receiving scheduling a resource for the ProSedirect communication from a base station. The terminal should be in aRRC CONNECTED state according to the mode 1 in order to transmit data.The terminal requests a transmission resource to the base station, andthe base station schedules a resource for scheduling assignment and datatransmission. The terminal may transmit a scheduling request to the basestation and may transmit a Buffer Status Report (ProSe BSR). The basestation has data which the terminal will perform the ProSe directcommunication and determines whether a resource for transmitting thedata is required.

2. Mode 2

The mode 2 is a mode for selecting a direct resource. The terminaldirectly selects a resource for the ProSe direct communication from aresource pool. The resource pool may be configured by a network or maybe previously determined.

Meanwhile, when the terminal includes a serving cell, that is, when theterminal is in an RRC_CONNECTED state with the base station or islocated in a specific cell in an RRC_IDLE state, the terminal isregarded to be in coverage of the base station.

If the terminal is located outside of the coverage, only the mode 2 isapplicable. If the terminal is located in the coverage, the mode 1 orthe mode 2 may be used according to setting of the base station.

If there are no exceptional conditions, only when the base station isconfigured, the terminal may change a mode from the mode 1 to the mode 2or from the mode 2 to the mode 1.

ProSe Direct Discovery (D2D Discovery )

The ProSe direct discovery represents a process used to discover whenthe ProSe enabled terminal discovers other neighboring ProSe enabledterminal and refers to D2D direction discovery or D2D discovery. In thiscase, an E-UTRA wireless signal through the PC 4 interface may be used.Hereinafter, information used for the ProSe direct discovery refers todiscovery information.

FIG. 7 illustrates a PC 5 interface for D2D discovery.

Referring to FIG. 7 , the PC 5 interface includes an MAC layer, a PHYlayer, and a ProSe Protocol layer being an upper layer. Permission forannouncement and monitoring of discovery information is handled in theupper layer ProSe Protocol. Contents of discovery information aretransparent to an access stratum (AS). The ProSe Protocol allows onlyvalid discovery information to be transferred to the AS forannouncement.

An MAC layer receives discovery information from the upper layer ProSeProtocol. An IP layer is not used for transmitting the discoveryinformation. The MAC layer determines a resource used in order toannounce the discovery information received from the upper layer. TheMAC layer makes and sends a protocol data unit (MAC PDU) to a physicallayer. An MAC header is not added.

There are two types of resource assignments for announcing the discoveryinformation.

1. Type 1

The type 1 is a method assigned so that resources for announcing thediscovery information are not terminal-specific and the base stationprovides resource pool configuration for announcing the discoveryinformation to the terminals. The configuration may be included in asystem information block (SIB) to be signaled in a broadcast scheme.Alternatively, the configuration may be included in a terminal specificRRC message to be provided. Alternatively, the configuration may bebroadcast-signaled or terminal-specific signaled of a different layerfrom the RRC message.

The terminal selects a resource from an indicated resource pool toannounce discovery information using the selected resource. The terminalmay announce discovery information through a resource optionallyselected during each discovery period.

2. Type 2

The type 2 is a method where resources for announcing the discoveryinformation are terminal-specifically assigned. A terminal in aRRC_CONNECTED state may request a resource for announcing a discoverysignal to the base station through a RRC signal. The base station mayassign a resource for announcing a discovery signal as an RRC signal. Aresource for monitoring the discovery signal in a configured resourcepool may be assigned in terminals.

With respect to a terminal in an RRC_IDLE state, a base station mayreport a type 1 resource pool for announcing the discovery signal as anSIB. Terminals where ProSe direct discovery is allowed use a type 1resource pool for announcing the discovery information in the RRC_IDLEstate. Alternatively, the base station 2) reports that the base stationsupports the ProSe direct discovery through the SIB but may not providethe resource for announcing the discovery information. In this case, theterminal should enter the RRC_CONNECTED state for announcing thediscovery information.

With respect to a terminal in an RRC_CONNECTED state, the base stationmay configure whether to use a type 1 resource pool or a type 2 resourcepool for announcing the discovery information through a RRC signal.

Vehicle-to-X (V2X) Communication

As described above, D2D operation generally provides various advantagesin that it supports signal transmission and reception between devicesadjacent to each other. For example, a D2D UE may perform datacommunication with a high transmission rate and low latency. Also, D2Doperation may disperse traffic concentrated at a base station, and if aUE performing a D2D operation acts as a relay, D2D operation may extendthe coverage of the base station. As an extension of the D2Dcommunication, vehicle-related communication including signaltransmission and reception between vehicles is particularly calledVehicle-to-X (V2X) communication.

In one example, the ‘X’ in the V2X represents pedestrian (communicationbetween a vehicle and a device carried by individual (for example,handheld UE carried by a pedestrian, cyclist, driver, or passenger),where, in this case, V2X may be expressed by V2P), vehicle(communication between vehicles, V2V), infrastructure/network(communication between a vehicle and a roadside unit (RSU)/network,where RSU is a transportation infrastructure entity, for example, anentity transmitting speed notifications implemented in an eNB or astationary UE, V2I/N). Also, in one example, for the convenience ofdescription of the proposed method, a (V2P communication-related) devicecarried by a pedestrian (or person) is called a “P-UE” while a (V2Xcommunication-related) device installed in a vehicle is called a “V-UE”.Also, in one example, the term ‘entity’ in this document may beinterpreted as P-UE, V-UE or RSU (/network/i nfrastructure).

A V2X UE may perform message (or channel) transmission on a predefined(or signaled) resource pool. Here, a resource pool may refer to apredefined resource(s) which enables a UE to perform a V2X operation (orwhich is capable of performing a V2X operation). At this time, aresource pool may also be defined in terms of time-frequency aspect

Meanwhile, various types of V2X transmission resource pools may bedefined.

FIG. 6 illustrates types of V2X transmission resource pools.

Referring to FIG. 6(a), V2X transmission resource pool#A may be aresource pool that allows (partial) sensing only. In the V2Xtransmission resource pool#A, a UE has to select a V2X transmissionresource after performing (partial) sensing, and random selection maynot be allowed. As shown in FIG. 6(a), a V2X transmission resourceselected by (partial) sensing is maintained semi-statically atpredetermined intervals.

In order for a UE to perform V2X message transmission on the V2Xtransmission resource pool#A, a base station may configure a (schedulingassignment decoding/energy measurement-based) sensing operation to beperformed (partially). This may be interpreted as not allowing ‘randomselection’ of a transmission resource on the V2X transmission resourcepool#A but may be interpreted as (allowing) performing (only) ‘(partial)sensing’ based transmission resource selection. The configuration may beset by the base station.

Referring to FIG. 6(b), the V2X transmission resource pool#B may be aresource pool that allows random selection only. In the V2X transmissionresource pool#B, a UE may not perform (partial) sensing but select a V2Xtransmission resource randomly from a selection window. In one example,different from a resource pool which allows (partial) sensing only, aresource pool which allows only random selection may set (or signaled)so that a selected resource may not be semi-statically reserved.

A base station may set not to perform a (scheduling assignmentdecoding/energy measurement-based) sensing operation so that a UE mayperform a V2X message transmission operation on the V2X transmissionresource pool#B. This may be interpreted as performing (/allowing) only‘random selection’ of a transmission resource on the V2X transmissionresource pool#B and/or not allowing ‘(partial) sensing’-basedtransmission resource selection.

Meanwhile, although not shown in FIG. 6 , there may exist a resourcepool which allows both (partial) sensing and random selection. A basestation may inform (the UE) that in such a resource pool, either of the(partial) sensing and random selection may be used to select a V2Xresource.

FIG. 7 illustrates a V2X transmission resource (re)selection(/reservation) method according to a partial sensing operation.

Referring to FIG. 7 , a UE (which denotes a P-UE in what follows) maydetermine (or trigger) (re)selection (or reservation) of a resource forV2X signal transmission (depending on whether a predetermined conditionis satisfied). For example, suppose the transmission resource(re)selection (or reservation) is determined or triggered at subframe#m. In this case, the UE may (re)select (or reserve) a resource for V2Xsignal transmission from within a subframe period ranging from thesubframe #m+T1 to #m+T2. In what follows, the subframe period rangingfrom the subframe #m+T1 to #m+T2 is called a selection window. Forexample, a selection window may comprise 100 consecutive subframes.

A UE may select at least Y subframes within a selection window ascandidate resources. In other words, a UE may have to consider at leastY subframes as candidate resources within the selection window. The Ymay be a predetermined value or may be determined by the network. Itshould be noted that how to select Y subframes within a selection windowmay be subject to issues of implementing a UE. In other words, supposethe Y value is 50. Then the UE may select which 50 subframes to selectamong 100 subframes comprising a selection window. For example, the UEmay select 50 subframes whose subframe number is an odd number fromamong the 100 subframes. Likewise, the UE may select 50 subframes whosesubframe number is an even number. Similarly, 50 subframes may beselected by an arbitrary rule.

Meanwhile, in order to (re)select (or reserve) a specific subframe amongthe Y subframes, for example, subframe #N (SF#N) as a V2X transmissionsubframe capable of transmitting a V2X signal, the UE may have to belinked to the subframe #N or sense at least one associated subframe. The(whole) subframe period defined for sensing is called a sensing window,which may comprise 1000 subframes, for example. In other words, asensing window may span 1000 milliseconds or 1 second. For example, theUE may sense subframes corresponding to subframe #N-100*k (where k maybe a set of elements in the range [1, 10] and may be preset ordetermined by the network) within the sensing window.

FIG. 7 illustrates a case in which k values are {1, 3, 5, 7, 10}. Inother words, the UE may sense subframe #N-1000, #N-700, #N-500, #N-300,and #N-100, infer/determine whether the subframe #N is used by other V2XUE (and/or whether relatively high interference (or interference largerthan a preset (or signaled) threshold value) exists on the subframe #N),and (finally) select the subframe #N according to the result. Since aP-UE is more sensitive to battery consumption than a V-UE, not all ofthe subframes within the sensing window are sensed but only part thereofis sensed, namely partial sensing is performed.

In one example, at the time of V2V communication, (A) a sensingoperation-based transmission resource selection procedure (or method)and/or (B) a V2V resource pool configuration (or signaling) procedure(or method) may be described as follows.

(A) Sensing operation-based transmission resource selection procedure(or method)

STEP 1: in the case of PSSCH resource (re)selection, if all of thePSCCH/PSSCH transmissions have the same priority, the entire resourcesmay first be considered as selectable resources.

STEP 2: Meanwhile, the UE may exclude a resource on the basis of atleast one of SA decoding and an additional condition.

The UE selects a V2X transmission resource after excluding a specificresource on the basis of scheduling assignment and an additionalcondition. At this time, if scheduling assignment and data associatedtherewith are transmitted from the same subframe, a method for excludinga resource on the basis of DM-RS reception power of the PSSCH may besupported. In other words, resources specified or reserved by decodedscheduling assignment and resources the PSSCH Reference Signal ReceivedPower (RSRP) received from data resources associated with the schedulingassignment of which exceeds a threshold value are excluded. Morespecifically, the PSSCH RSRP may be defined as a linear average of powerdistribution over Resource Elements (REs) carrying DM-RSs associatedwith the PSSCH within Physical Resource Blocks (PRBs) indicated by thePSCCH. The PSSCH RSRP may be measured with respect to the antennaconnecting unit of the UE. The scheduling assignment may include a 3-bitPPPP field.

The threshold value may be expressed as a function of priorityinformation. For example, the threshold value may be dependent on thepriority information of a transmission block and priority information ofdecoded scheduling assignment The threshold may be set as a valuestarting from -128 dBm up to 0 dBm in 2 dBm units. A total of 64threshold values may be predefined.

It may be assumed that the UE decodes scheduling assignment at thesubframe #m+c belonging to the sensing period, and the same frequencyresource is reserved by the scheduling assignment at the subframe#m+d+P*i. As described above, P may be a fixed value of 100. i may beselected from the range of [0, 1, ..., 10], which may be set in acarrier-specific manner by the network or predetermined. If i = 0, itindicates that no frequency resources are intended to be reserved. i maybe set by a 10-bit bitmap or by a four-bit field within schedulingassignment.

If a candidate semi-static resource X collides with a resource Yreserved by scheduling assignment by another UE at the period P*I andsatisfies a condition for exclusion, the UE may exclude the candidatesemi-static resource X. The I represents the value of i signaled byscheduling assignment.

If the remaining resources after excluding resources through schedulingassignment decoding, sensing process, and so on is less than 20% of thetotal resources within a selection window, the UE increases thethreshold value (for example, by 3 dB) and again performs the process ofexcluding resources, where the process may be performed until theremaining resources is more than 20% of the total resources within theselection window. The total resources within the selection windowrepresent the resources that the UE has to consider as possiblecandidate resources.

Meanwhile, during the process of selecting a V2X transmission resourceafter a specific resource is excluded, if the UE’s counter reaches 0,the current resources may be maintained with a probability of p, and thecounter may be reset. In other words, resources may be reselected with aprobability of 1-p.

The carrier-specific parameter p may be preset and take a value from [0,0.2, 0.4, 0.6, 0.8].

The UE measures the remaining PSSCH resources except for specificresources, ranks the remaining PSSCH resources in terms of totalreceived energy, and selects a subset. The subset may be a set ofcandidate resources having the lowest reception energy. The size of thesubset may amount to 20% of the total resources within a selectionwindow.

The UE may select one resource randomly from the subset.

When only one transmission block is transmitted from one subframe, theUE may select M consecutive sub-channels, and the average of energymeasured at each sub-channel may become the energy measurement value ofeach resource.

Meanwhile, when a Transmission Block (TB) is transmitted from twosubframes, the following resource selection may be supported.

First, one resource which uses a mechanism defined for the case of a TBtransmitted from one subframe may be selected

And other resources may be selected randomly under the followingconditions. A selected resource should be neither the same subframe asthe first resource nor a subframe excluded from resource selection.Moreover, SCI should be able to indicate a time gap between two selectedresources.

If no resource satisfies a condition for selecting a second resource, aTB may be transmitted by using the first resource only.

STEP 3: the UE may select a V2X transmission resource among theresources not excluded.

(B) V2V resource pool configuration (signaling) procedure (or method)

First, if resources are configured so that SA and data are alwaystransmitted from the same subframe, the UE is not expected to transmitmixed PSCCHs from different subframes.

In a pool where the UE is configured to transmit SA and data always fromRBs adjacent to the same subframe, among sub-channels selected for datatransmission, the sub-channel having the lowest index may be used for SAtransmission.

In the case of a pool in which the UE is configured to transmit SA anddata from RBs not adjacent to the same subframe, the number of SAcandidate resources in the SA pool may be the same as the number ofsub-channels in the associated data pool. Among the SA resourcesselected for data transmission, the SA resource associated with thelowest index may be used for SA transmission.

The UE may perform resource selection/reselection at TTI m (≥ n). Here,TTI m may represent reception time of a TB.

Regarding resource reselection, the UE has to consider candidateresources available in the period of [m+T1, m+T2]. Here T1 is aUE-specific parameter, and T1 ≤ [4]. Also, T2 may be a UE-specificparameter, and 20 ≤ T2 ≤ 100. Here the selected T2 has to satisfy thelatency requirement.

Also, a sensing window may change as [m-a, m-b). (Here, a = b+1000 and b= 1).

In the case of a pool in which the UE is configured to always transmitSA and data from RBs adjacent to the same subframe, a resource pool maycomprise one or more sub-channels in the frequency domain. Here, asub-channel may be composed of a group of RBs adjacent to the samesubframe. Moreover, the size of a sub-channel in the resource pool maybe set by a base station (for example, eNB) or a predetermined value.Here, candidate resources of a sub-channel may be selected from a subset{5, 6, 10, 15, 20, 25, 50, 75, 100}.

In the case of a pool in which the UE is configured to transmit SA anddata from RBs not adjacent to the same subframe, a resource pool maycomprise one or more sub-channels in the frequency domain. Here, asub-channel may be composed of a group of RBs adjacent to the samesubframe. Moreover, the size of a sub-channel in the resource pool maybe set by a base station (for example, eNB) or a predetermined value.Here, the number of sub-channels may not be more than 200, and theminimum candidate size may not be less than 4.

The UE may select an integer number of adjacent sub-channels fortransmission and may not decode more than 100 RBs in one subframe.Moreover, the UE may not decode more than 10 PSSCHs in one subframe.

The SA pool may be overlapped with an associated data pool. Moreover,the SA pool may also be overlapped with a non-associated data pool.

In the case of a pool in which the UE is configured to transmit SA anddata from RBs adjacent to the same subframe, a resource pool may becomposed of N consecutive PRBs. Here, N may be the same as (size of asub-channel x number of sub-channels).

The V2V pool may be defined so that bitmaps are repeatedly mapped ontoall of the subframes except for skipped SLSS subframes. Here, the lengthof a bitmap may be 16, 20, or 100. The bitmap may define which subframeis allowed for V2V SA/data transmission and/or reception with respect toa pool.

Meanwhile, if resource reselection is triggered, the UE may reselectresources related to all transmissions corresponding to one TB. Here, SAmay schedule transmission corresponding to one TB. Also, PSSCH-RSRPmeasured in a TTI occurred before reception of associated SA decodedsuccessfully may be applied. Here, the number of transmission for one TBmay be 1 or 2. Additionally, each SA may indicate time/frequencyresources for all of the data transmission corresponding to the same TB.

In what follows, the present invention will be described

The proposed methods described below deal with a situation in which aV2X UE(s) (re)reserves (or selects) its own resource(s) related to V2Xmessage transmission. In this situation, the present invention provides(A) a method for efficiently defining boundaries in the time domain inwhich a sensing operation is performed and (B) a method for efficientlysupporting retransmission (RE-TX) of V2X message(s) omitted (or stopped)as the sensing operation is performed. Here, as one example, the word“sensing” in this document may be interpreted as RSRP measurementoperation (for example, S-RSRP) with respect to a (predefined orsignaled) Reference Signal (RS) (on the PSSCH scheduled by the PSCCHwhich has been successfully decoded) and/or energy measurement operation(for example, S-RSSI) with respect to a (sub)channel, or decodingoperation with respect to a predefined (signaled) channel (for example,Physical Sidelink Control Channel (PSCCH)). In one example, in thepresent invention, the word “duration” (and/or “period”) may be extendedto be interpreted as “range (or window)”.

[Proposed Rule#1] The boundary (or position) of a time region (orperiod) in which a sensing operation is performed (for each V2X UE(s))may have the form (or characteristic) of “UE-specific (time) boundary”.Here, in one example, the boundary (or position) of the time region (orperiod) in which a (resource (re)reservation (or selection)-related)sensing operation of a specific V2X UE is performed may be defined as“V2X message TX time (SF#K)” (of the corresponding V2X UE). When thisrule is applied, in one example, the V2X UE performs a sensing operationat the remaining (resource) time points except for the (resource) timepoint at which the V2X UE (actually) performs a V2X message TX operationon the resource period ranging from “SF#(K-D) to SF#K (or the resourceperiod ranging from SF#(K-1-D) to SF#(K-1)) (where, in one example, “D”represents a predefined (or signaled) ‘sensing duration’)” and then(re)reserves (or selects) its own resource(s) related to V2X message TX.Here, as another example, the V2X UE skips (or stops) (last)transmission (of its V2X message) on the ‘SF#K’ (according to apredefined rule) (if needed), performs sensing (measurement) of up to(SF#K) resources of the V2X UE (or previously reserved (or selected)resources), and immediately performs optimal re-reservation (orselection) of resources (and/or immediately transmits a V2X message byusing the re-reserved (or selected) resources). Here, as a still anotherexample, in the case of a V2X UE performing a sensing operation in theresource period, the V2X UE may perform (sensing result-based) resource(re)reservation (or selection) on the resource period ranging from“SF#(K+1) to SF#(K+1+R) (or a resource period ranging from SF#K toSF#(K+R), where “R” represents a predefined (or signaled) ‘TX resource(re)selection duration’)”.

For the convenience of understanding, that the boundary of a time regionin which a sensing operation (for each V2X UE(s)) is performed accordingto the proposed rule#1 takes the form (or characteristic) of a“UE-specific (time) boundary” may be described with reference to relateddrawings as follows.

FIG. 8 is a flow diagram illustrating a method for performing V2Xcommunication based on a UE-specific sensing period according to oneembodiment of the present invention.

Referring to FIG. 8 , a UE may select a resource with which to performV2X communication by performing sensing during a UE-specific sensingperiod S810. Here, the UE’s performing sensing during a specific period(namely, UE-specific sensing period (or UE-specific sensing window)) andselecting a resource with which to perform V2X communication may bedescribed from a viewpoint that (A) the period during which the UEperforms sensing (namely, a sensing window) is UE-specific and from aviewpoint that (B) the period during which the UE performs sensing is 1second (namely, a period corresponding to 1000 subframes, where eachsubframe occupies a period of 1 ms) and the 1 second corresponds to upto SPS period (or maximum (possible) resource reservation period) length(namely [N-1000, N-1]).

(A) First, selection of a resource to perform V2X communication may bedescribed as follows from a viewpoint that the period in which a UEperforms sensing (namely a sensing window) is UE-specific.

As described above, the UE may select a resource to perform V2Xcommunication by performing sensing, where UEs may have differentperiods during which sensing is performed (namely UE-specific sensingperiods) Here, having a UE-specific sensing period does not mean thatsensing time itself is different for each UE but the position of thesensing period (namely a sensing window) is different for each UE.

In other words, the boundary of a time region in which a sensingoperation is perform (for each V2X UE(s)) may have the form (orcharacteristic) of a “UE-specific (time) boundary”. In other words, anenergy measurement window is UE-specific (in other words, in the caseof″[N-A, N-B]” energy sensing (or measurement) period, the N value isUE-specific), which is described with reference to related drawings asfollows.

FIG. 9 illustrates an example of a UE-specific sensing window.

Referring to FIG. 9 , each UE, namely ‘UE 1’ and ‘UE 2’ have a sensingwindow spanning a different time period, and sensing windows may bedefined for the respective UEs at different times.

More specifically, if an upper layer of the UE makes a request at aspecific subframe (in what follows, subframe N), the UE may determine aset of resources that have to be transmitted to the upper layer inconjunction with V2X message transmission (for example, PSSCHtransmission).

Afterwards, the UE monitors during a specific sensing period (excludingsubframes in which the UE performs transmission) (for example, subframeN-1000, N-999, N-998, ..., up to N-1). Here, that the UE monitors aspecific sensing period (for example, subframe N-1000, N-999, ..., up toN-1) with respect to the subframe N determined by the upper layer of theUE itself means that the sensing window in which the UE performsmonitoring is determined by the corresponding UE.

To describe an example of FIG. 9 , in the case of UE 1, it may beassumed that the upper layer of UE 1 generates a request at N_(_UE1). Inthis case, the sensing period of UE 1 (namely, a sensing window) spansthe subframe N_UE1-1000, N_UE1-999, ..., up to N_UE1-1, and the sensingwindow in this case is specific to the UE 1 as shown in FIG. 9 . In thesame manner, in the case of UE 2, it may be assumed that the upper layerof UE 2 generates a request at N__(UE2). In this case, the sensingperiod of UE 2 (namely, a sensing window) spans the subframe N_UE2-1000,N_UE2-999, ..., up to N_UE2-1, and the sensing window in this case isspecific to the UE 2 as shown in FIG. 9 .

Afterwards, the UE may select a resource with which to perform V2Xcommunication on the basis of S-RSSI measured within the aforementionedsubframes, namely N-1000, N-999, N-998, ..., N-1 and the decoded PSCCH.Here, a specific example in which the UE selects a resource with whichto perform V2X communication is the same as described above.

(B) The descriptions given below are based on the viewpoint that theperiod during which the UE performs sensing is 1 second (namely a periodof 1000 subframes) and the 1 second corresponds to the maximumSemi-Persistent Scheduling (SPS) (or maximum (possible) resourcereservation period) length (namely [N-1000, N-1]).

In one example, if a V2X UE uses a sensing result obtained by monitoringthe period comprising ‘SF#(N-A), SF#(N-A+1), ..., SF#(N-B) (or SCPERIOD#(N-A), SC PERIOD#(N-A+1), ..., SC PERIOD#(N-B)) (A≥B (forexample, the ‘B’ value may be a positive integer larger than ‘0’ bytaking into account the processing time for resource (re)selection)) for(V2X message TX-related) resource (re)reservation (or selection) in atriggered ‘SF#N’ (or ‘SC PERIOD#N’), the “MONITORING WINDOW SIZE(namely, ‘(A-B)’)” may be set to the maximum value of the times at whichresource (re)reservation (or selection) occurs (which may be interpretedas the interval between reserved resources, for example). In oneexample, the corresponding V2X UE selects its transmission resourcesfrom the period of ‘SF#(N+C), SF#(N+C+1), ..., SF#(N+D) (or SCPERIOD#(N+C), SC PERIOD#(N+C+1), ..., SC PERIOD#(N+D)) (D≥C (forexample, the ‘C’ value may be a positive integer larger than ‘0′ bytaking into account the processing time related to PSCCH/PSSCHgeneration))’. As a specific example, if resource (re)reservation (orselection) is performed every 500 milliseconds, (by taking into accountthat the time length of a transmission resource (latency requirement) is100 ms) ‘(A-B)’ may become 400 ms (here, for example, the ‘400 ms’ maybe interpreted as the remainder after subtracting one predefined ‘SCPERIOD (100 ms)’ (latency requirement) from ‘500 ms’). Also, in oneexample, the corresponding ‘400 ms’ period may be interpreted as aperiod ranging from ‘SF#(N-500MS)’ to ‘SF#(N-100MS)’. In other words,the ‘SENSING DURATION’ (or ‘(A-B)’) may become a function of predefined(or preset) ‘resource (re)reservation (or selection) period’ (or it maybe interpreted as performing a ‘sensing operation’ during the timeperiod derived from the ‘resource (re) reservation (or selection)period). To summarize, in one example, since the same resource will beselected (or used) until ‘resource re-reservation (or selection)’ isperformed, it may be meaningful to sense the resource right before thecurrent (resource re-reservation (or selection)’) period, but it is notrequired to sense the resource before the time at which the ‘resourcere-reservation (or selection)’ necessarily occurs. Here, in one example,such a rule may be particularly useful when the SA/DATA (pool) isimplemented as a ‘TDM structure’.

As another example, it is assumed that the V2X UE(s) performs ‘SA (orPSCCH)’ transmission related to the ‘DATA (or PSSCH)’ transmissionassociated with the “SF#(N+D)’ (for example, D≥C) in the ‘SF#(N+C)’.Here, in one example, the ‘SF#N’ may be assumed (or interpreted) as thetime at which (according to a predefined rule (or signaling)) the‘RESOURCE (RE)SELECTION’ operation is performed and/or the periodranging from the ‘SF#(N-A)’ to the SF#(N-B)’ (for example, A > B > 0)may be assumed (or interpreted) as the region which provides a sensingresult referenced when ‘SA (or PSCCH) (‘SF#(N+C)’) and/or DATA (orPSSCH) (‘SF#(N+D)’) RESOURCE (RE)SELECTION operation is performed (or inwhich sensing is performed). Here, in one example, when ‘POTENTIAL DATA(or PSSCH)’ transmission related to other TB on the ‘SF#(N+E)’ isperformed in the ‘SF#(N+D)’ (for example, D < E), the V2X UE may informof the intent of whether to reuse a ‘(frequency) resource’ (used for‘DATA (or PSSCH)’ transmission on the ‘SF#(N+D)’) through a (predefined(or signaled)) channel (for example, ‘SA (or PSCCH)’ (SF#(N+C)’) (orthrough ‘DATA (or PSSCH)’). Here, in one example, a field to which‘(E-C)’ value (or ‘(E-D)’ value or ‘E’ value) is (additionally)transmitted may be (newly) defined on the ‘SA (or PSCCH)’ (‘SF#(N+C)’)used for the corresponding use. Here, in one example, ‘(E-C)’ value(E_CGAP) (or ‘(E-D)’ value (E_DGAP)) (or ‘E’ value (E_GAP)) may beinterpreted as an interval between ‘SA (or PSCCH)’ (‘SF#(N+C)’)transmission time point and ‘NEXT TB’ related (POTENTIAL) DATA (orPSSCH) transmission time point (or an interval between the ‘DATA (orPSSCH)’ transmission time point scheduled from ‘SA (or PSCCH)’(‘SF#(N+C)’) and the (POTENTIAL) ‘DATA (or PSSCH) transmission timepoint related to the ‘NEXT TB’) or ‘V2X MESSAGE GENERATION (or TX)PERIODICITY’. Here, in one example, the ‘SENSING WINDOW SIZE’ (forexample, ‘(B-A)’) of the V2X UE may be determined (or configured)according to the following (partial) rule. Here, in one example,‘E-CGAP’ (or E_DGAP or E_GAP) related (maximum (or minimum)) value maybe set (or signaled) to SINGLE VALUE’ or ‘MULTIPLE VALUE(s)’ (in a‘UE-COMMON’ or ‘UE-SPECIFIC’ manner from the network or a (serving) basestation) or may be regarded (or assumed) to be the same as the V2X UE’s(maximum (or minimum)) ‘MESSAGE GENERATION (or TX) PERIODICITY’ .

(Rule#A) (A) ‘E_CGAP’ (or E_DGAP or E_GAP) related (maximum (orminimum)) value and/or (B) (maximum (or minimum)) MESSAGE GENERATION (orTX) PERIODICITY’ value may be considered (or determined) as the ‘SENSINGWINDOW SIZE’. As another example, the ‘SENSING WINDOW SIZE’ may be setto a predefined (or signaled) (specific) value irrespective of (A)‘ECGAP’ (or E_DGAP or E_GAP) related (maximum (or minimum)) value and/or(B) (maximum (or minimum)) ‘MESSAGE GENERATION (or TX) PERIODICITY’value. Here, in one example, if the aforementioned rule is applied, evenwhen the V2X UE performs ‘V2X MESSAGE’ transmission having a(relatively) long ‘MESSAGE GENERATION (or TX) PERIODICITY’, a sensingoperation may be performed by using a (relatively) small ‘SENSING WINDOWSIZE’ (which may be interpreted as a kind of ‘PARTIAL. (or LIMITED)REGION SENSING’). In one example, in the Rule#A, the ‘SENSING WINDOWSIZE’ may be set in a ‘UE-COMMON’ (or ‘UE-SPECEFIC’) manner.

(Rule#B) A predefined (or signaled) ‘(V2X) SPS PERIODICITY’ value may beconsidered (or determined) as the ‘SENSING WINDOW SIZE’. Here, in oneexample (in which the corresponding rule is applied), if a plurality ofdifferent ‘SPS configurations (or processes)’ are set (or signaled) tothe ‘SPS PERIODICITY’, it may be interpreted (or considered) that adifferent ‘SENSING WINDOW SIZE’ is applied to each ‘SPS configuration(or process)’. As another example, when a plurality of ‘SPSconfigurations (or processes or (transmission) operations) havingdifferent ‘(V2X) SPS PERIODICITIES’ are set (or signaled or permitted),the maximum (or minimum) value among the corresponding ‘(V2X) SPSPERIODICITIES’ is determined (or derived) as the ‘(COMMON) SENSINGWINDOW SIZE’, which may also be applied commonly to the plurality of‘SPS configurations (or processes or (transmission) operations). In oneexample, in the Rule#B, the ‘SENSING WINDOW SIZE’ may be set in a‘UE-SPECIFIC’ (or ‘UE-COMMON’) manner.

Here, the SPS period may be determined as in the resource reservationfields of Sidelink Control Information (SCI) format 1 of Table 1 asshown below.

TABLE 1 Resource reservation field in the SCI format 1 Indicated value XCondition ‘0001’, ‘0010’, ..., ‘1010’ Decimal number corresponding tothe field The upper layer is different. Resources for transmitting TBsare maintained, and the value of X is such that 1 ≤ X ≤ 10. ‘1011’ 0.5The upper layer is different. Resources for transmitting TBs aremaintained, and the value of X is 0.5. ‘1100’ 0.2 The upper layer isdifferent. Resources for transmitting TBs are maintained, and the valueof X is 0.2. ‘0000’ 0 The upper layer is different. Resources fortransmitting TBs are not maintained. ‘1101’, ‘1110’, ‘1111’ Reserved -

Here, a receiving UE (RX UE) may figure out the resource reservationperiod of the final transmitting UE (TX UE) on the basis of the valuesthat may be signaled to the RESOURCE RESERVATION field of the SCI formatshown in table 1.

At this time, by multiplying the value of the resource reservation fieldby 100, the RX UE may determine the “resource reservation periodcandidate value’ that may be configured by the TX UE. For example, ifthe value of the resource reservation field is ‘0001’, the resourcereservation period may be 100 ms while, if the value of the resourcereservation field is ‘0010’, the resource reservation period may be 200ms. In the same manner, if the value of the resource reservation fieldis ‘1010’, the resource reservation period may be 1000 ms.

To summarize, the RX UE may figure out that the “resource reservationperiod candidate” values which may be set by the TX UE by multiplyingthe value of the resource reservation field by 100 are “20, 50, 100,200, 300, 400, 500, 600, 700, 800, 900, 1000 ms”, and accordingly, themaximum value of the SPS period may have the value of 1000 ms (namely 1s).

As described above, the period in which a UE performs sensing (namely asensing window of the UE) may have the maximum SEMI-PERSISTENTSCHEDULING (SPS) period (or the maximum (possible) resource reservationperiod), and accordingly, the period in which the UE performs sensing(namely a sensing window) may be 1000 ms (namely 1s0 which is themaximum value of the SPS period.

Referring again to FIG. 8 , the UE may perform V2X communication byusing the selected resources S820. As described above (or below), the UEmay select a subframe within a selected window on the basis of a sensingresult obtained by performing sensing during a UE-specific sensingperiod, determine transmission reservation resources on the basis ofselected subframes, and perform V2X communication on the reservedresources. Since specific example in which the UE performs V2Xcommunication on the basis of selected resources is the same asdescribed above (or below), specific details will be omitted.

Meanwhile, end-to-end latency has to be taken into account for V2Xcommunication. In other words, when the UE transmits a packet generatedin the upper layer, not only the time required to send a packetgenerated in the upper layer down to the physical layer but also thetime for the RX UE to receive the packet and send the received packet upto the upper layer of the RX UE has to be considered. Therefore, how toconfigure a period during which the UE selects a resource for performinga V2X message transmission, namely a selection window to select atransmission resource becomes of importance. In what follows, a methodfor configuring a selection window will be described with reference torelated drawings.

FIG. 10 is a flow diagram illustrating a method for configuring aselection window according to one embodiment of the present invention.

A UE may select a resource (or subframe and in what follow, a resourceand a subframe may be used interchangeably for the convenience ofdescription) with which to perform V2X communication within a rangesatisfying a latency requirement S1010. At this time, the UE may selectthe resource by configuring a selection window within a range satisfyingthe latency requirement, the V2X communication may be performed in unitsof multiple sub-channels, and a resource for performing the V2Xcommunication may be selected on the basis of the sensing resultobtained by performing in units of sub-channels the size of whichcorresponds to the size of the multiple sub-channels. The sensing regionin which the sensing is performed may have the size corresponding tothat of the plurality of sub-channels. Moreover, the UE may also performsensing by using the energy measurement average value of sub-channelsbelonging to the multiple sub-channels.

To summarize, the UE may not only select the resource by configuring aselection window within a range satisfying the latency requirement butalso perform sensing in units of multiple sub-channels when the V2Xcommunication is performed in units of multiple sub-channels. A specificexample in which sensing is performed in units of multiple sub-channelswhen the V2X communication is performed in units of multiplesub-channels will be described later.

In what follows, an example in which the UE selects a transmissionresource within a range satisfying the latency requirement will bemainly described.

The UE may (configure a selection window and) select a transmissionresource (or subframe) within a range satisfying the latencyrequirement. Here, the UE may assume that a set of neighboringsub-channels (for example, LsubCH) in the V2X resource pool (forexample, PSSCH resource pool) belonging to a specific period (forexample, [n+T1, n+T2]) correspond to one candidate subframe (resource).At this time, selection of information (for example, T1 and T2) fordetermining the specific period may depend on how the UE is implemented.T1 may have a value less than or equal to 4 while T2 may have a valuenot less than 20 and not more than 100. In particular, UE’s selection ofT2 has to satisfy the latency requirement

For example, ‘SENSING DURATION (D)’ and/or ‘TX RESOURCE (RE)SELECTIONDURATION (R)’ may be (implicitly) assumed to be the same as the ‘V2XMESSAGE GENERATION PERIOD’ (and/or ‘(SERVICE) LATENCY REQUIREMENT’)(and/or depending on the ‘V2X MESSAGE GENERATION PERIOD’ (and/or‘(SERVICE) LATENCY REQUIREMENT’ and/or ‘(V2X MESSAGE (or TB)) or ‘PPPP’(for example, when a (partly) different ‘PPPP’ value is set (orpermitted) for each V2X MESSAGE (or TB) having a different ‘(SERVICE)LATENCY REQUIREMENT’), may be assumed (or changed) differently) and/orassume a predefined (or signaled) specific value (for example, thecorresponding rule may be interpreted that ‘TX RESOURCE (RE)SELECTIONDURATION (R)’ is configured to satisfy the ‘(SERVICE) LATENCYREQUIREMENT’). Here, in one example, (in particular, in the lattercase), the ‘SENSING DURATION (D)’ and ‘TX RESOURCE (RE)SELECTIONDURATION (R)’ may (always) be set (or considered) to have the same valueor may be defined to have an independent (or different) value. Asanother example, the boundary of the time region in which the (resource(re)reservation (or selection)-related) sensing operation of a specificV2X UE is performed may be defined as “V2X MESSAGE GENERATION TIME” (ofthe corresponding V2X UE). As a yet another example, when the ‘(TX)PROCESSING TIME’ (of the V2X UE) is considered, the time point obtainedby adding (or subtracting) a predefined (or signaled) offset to (orfrom) the ‘boundary criterion of a time region in which a sensingoperation (related to resource (re)reservation (or selection)) isperformed’ described above (for example, ‘V2X MESSAGE TX TIME’ and ‘V2XMESSAGE GENERATION TIME’) may become the final ‘boundary criterion of atime region in which a sensing operation is performed’. As a specificexample, the V2X UE performs a sensing operation at the remaining(resource) time points except for the (resource) time point at which theV2X UE itself (actually) performs the V2X MESSAGE TX operation in theresource period ranging from “SF#(K-D-S) to SF#(K-S) (or in the resourceperiod ranging from SF#(K-1-D-S) to SF#(K-1-S) (where, in one example,“D” and “S″ represent the predefined (or signaled) ‘SENSING DURATION’and ‘(TX) PROCESSING TIME’ (of the V2X UE), respectively” and then(re)reserve (or select) a V2X MESSAGE TX-related resource(s) of the V2XUE itself (in the resource period ranging from “SF#(K+1) to SF#(K+1+R)(or from SF#K to SF#(K+R)) (where, in one example, “R” represents thepredefined (or signaled) ‘TX RESOURCE (RE)SELECTION DURATION’)).

Afterwards, the UE may perform V2X communication by using the selectedresource S1020. Here, as described above, the selected resource mayindicate the resource determined on the basis of a selection windowconstructed within a range satisfying the LATENCY REQUIREMENT (in otherwords, a resource on the selection window satisfying the latencyrequirement). Also, as described above (or below), the UE may select asubframe within the selection window on the basis of a sensing resultobtained by performing sensing in a UE-specific sensing period,determine transmission reservation resources on the basis of theselected subframe, and perform V2X communication on the reservedresource. Since a specific example in which the UE performs V2Xcommunication on the basis of a selected resource is the same asdescribed above (or below), specific details will be omitted.

FIGS. 11 and 12 illustrate the proposed rule#1.

FIGS. 11 and 12 assume that (for each V2X UE(s)) a V2X message isgenerated periodically (for example, ‘100 ms’). Also, in one example, itis assumed that the ‘SENSING DURATION (orTX RESOURCE (RE)SELECTIONDURATION)’ and ‘V2X MESSAGE TX related repetition number’ are set to‘100 ms’ and ‘1’, respectively. In an additional example, FIG. 11illustrates a case in which a V2X UE performs a sensing operation at theremaining (resource) time points except for the (resource) time point atwhich the V2X UE (actually) performs a V2X message TX operation on the“resource period ranging from SF#(K-100) to SF#K” and then re-reserves(or selects) the V2X message TX-related resource(s) on the “resourceperiod ranging from SF#(K+1) to SF#(K+101)” by using the correspondingsensing result. FIG. 12 illustrates a case in which a V2X UE performs asensing operation at the remaining (resource) time points except for the(resource) time point at which the V2X UE (actually) performs a V2Xmessage TX operation on the “resource period ranging from SF#(K-1) toSF#(K-101)” and then re-reserves (or selects) the V2X message TX-relatedresource(s) on the “resource period ranging from SF#(K+1 ) toSF#(K+101)” by using the corresponding sensing result. In one example,in FIGS. 11 and 12 , “transmission of the (N+1)-th V2X message’ isperformed through a reselection resource (for example, SF#(K+Z+100)).

FIGS. 13 and 14 illustrate determining a re-reservation (or selection)resource and performing a V2X message immediately by using there-reserved (or selected) resource.

More specifically, FIGS. 13 and 14 illustrate respectively a case inwhich, under the same situation as in FIGS. 11 and 12 , a V2X UE skips(or stops) transmission of a V2X message on the ‘SF#K’ (according to apredefined rule), senses (or measures) up to the resource (SF#K) thathas been used by the V2X UE (or reserved (or selected) previously), anddetermines the optimal re-reserved (or selected) resource andimmediately performs transmission of a V2X message by using there-reserved (or selected) resource. Here, in one example, ‘transmissionof the (N+1 )-th V2X message’ is performed through the reselectionresource (for example, SF#(K+Z+100)).

[Proposed Rule#2] For the purpose of sensing (or measuring) a resourceused (in the Proposed Rule#1) (or reserved (or selected) previously), askipped (or stopped) V2X message transmission (for example, in the casesof FIGS. 13 and 14 , ‘the N-th V2X message transmission’) may bere-transmitted according to the following (partial) rule.

(Example#2-1) If the ‘(SERVICE) LATENCY REQUIREMENT’ condition may besatisfied when the ‘skipped (or stopped) V2X message’ is re-transmittedthrough a re-reserved (or selected) resource after resourcere-reservation (or selection) is performed according to a ‘sensing(measurement) result’ and a ‘predefined (re-reservation (or selection))criterion (or rule)’ (without consideration to the retransmission of the‘skipped (or stopped) V2X message), it may be defined so thatretransmission of the ‘skipped (or stopped) V2X message’ is performed(immediately) (by using the corresponding re-reserved (or selected)resource). On the other hand, if the ‘(SERVICE) LATENCY REQUIREMENT’ isnot satisfied when retransmission of the ‘skipped (or stopped) V2Xmessage’ is performed through the re-reserved (or selected) resource, itmay be defined so that retransmission of the ‘skipped (or stopped) V2Xmessage’ (by using the corresponding re-reserved (or selected) resource)is not performed. As a specific example, in the cases of FIGS. 13 and 14, since the ‘(SERVICE) LATENCY REQUIREMENT (100 ms)’ may be satisfiedwhen retransmission of the ‘skipped (or stopped) V2X message (SF#K)’ isperformed through the re-reserved (or selected) resource (SF#(K+Z)),retransmission of the ‘skipped (or stopped) V2X message’ is performedimmediately (through the re-reserved (or selected) resource (SF#(K+Z)).

(Example#2-2) It may be defined so that the V2X UE performs resourcere-reservation (or selection) by taking into account only the ‘candidateresources’ which enable retransmission of the ‘skipped (or stopped) V2Xmessage’ to satisfy the ‘(SERVICE) LATENCY REQUIREMENT’. When this ruleis applied, for example, the V2X UE finally re-reserves (or selects) theoptimal resource which satisfies a predefined (re-reservation (orselection)) criterion (or rule) among the corresponding ‘candidateresources’. Here, in one example, through the corresponding finalre-reserved (or selected) resource, not only retransmission of the‘skipped (or stopped) V2X message’ but also transmission of a V2Xmessage(s) (to be generated) afterwards is performed. The rule describedabove may guarantee retransmission of the ‘skipped (or stopped) V2Xmessage’ with a high probability. To guarantee the operation describedabove, the region for ‘TX RESOURCE (RE)SELECTION DURATION (R)’ may bereduced. Through this scheme, only those resources close to the current(skipped (or stopped)) transmission time may be selected so that the(skipped (or stopped)) V2X message(s) is retransmitted while the‘(SERVICE) LATENCY REQUIREMENT’ is satisfied. In this case, the regionfor ‘SENSING DURATION (D)’ may also be (accordingly) reduced.

(Example#2-3) It may be defined so that a resource (or pool) for (only)retransmission of a (previously) ‘skipped (or stopped) V2X message’ isconfigured (or signaled) independently (or additionally) or a resourcefor retransmission of the ‘skipped (or stopped) V2X message’ may beselected additionally according to the following predefined (orsignaled) (partial) rule (or criterion). In one example, (in the lattercase) the corresponding resource selected additionally may be usedtemporarily (or limitedly) only for retransmission of a (previously)‘skipped (or stopped) V2X message’.

(Example#2-3-1) It may be defined so that the V2X UE selects anadditional (retransmission) resource by taking into account only the‘candidate resources’ which enable retransmission of the ‘skipped (orstopped) V2X message’ to satisfy the ‘(SERVICE) LATENCY REQUIREMENT’. Inanother example, it is not retransmission of the ‘skipped (or stopped)V2X message’ but resource re-reservation (or selection) for transmissionof a ‘V2X message(s) (to be generated) afterwards’ may be performedwithin a predefined (or signaled) ‘TX RESOURCE (RE)SELECTION DURATION’.Here, a resource re-reserved (or selected) for this use may be excludedfrom candidate resources for retransmission of the ‘skipped (or stopped)V2X message’ (although the re-reserved (or selected) resource maysatisfy the ‘(SERVICE) LATENCY REQUIREMENT’ when retransmission of the‘skipped (or stopped) V2X message’ is performed). In other words, theresource for transmission of a ‘V2X message(s) (to be generated)afterwards’ may be regarded as having a (relatively) higher prioritythan the resource for retransmission of the ‘skipped (or stopped) V2Xmessage’ (or transmission of a ‘V2X message(s) (to be generated)afterwards’ may be interpreted to be performed through the (most)optimal resource which satisfies a predefined (re-reservation (orselection)) criterion (or rule)).

[Proposed Rule#3] If one V2X message is transmitted ‘Q’ times (accordingto the proposed rule#1), the boundary of a time region in which a(resource (re)-reservation (or selection)-related) sensing operation isperformed may be defined according to the following (partial) criterion(or rule). Here, the ‘Q’ value may be a positive integer larger than 1.In what follows, for the convenience of description, it is assumed that(one) V2X message is ‘transmitted two times (for example, SF#(N+K1) andSF#(N+K1))’.

(Example#3-1) (If it is not the case that (one) V2X message istransmitted (repeatedly) through multiple SFs and/or independentresource allocation is made on each SF) the first (or last) ‘repeatedtransmission timing’ (or ‘SF’) may be defined as the boundary of a timeregion in which a (resource (re)-reservation (or selection)-related)sensing operation is performed. As a specific example, if the first‘repeated transmission timing’ (or ‘SF’) (for example, SF#(N+K1)) isdesignated as the boundary of a time region in which a sensing operationis performed, the V2X UE performs a sensing operation at the remaining(resource) time points except for the (resource) time point at which theV2X UE (actually) performs the V2X message TX operation on the “resourceperiod ranging from SF#(N+K1-D) to SF#(N+K1) (or from SF#(N+K1-1-D) toSF#(N+K1-1)) (where “D” represents the predefined (or signaled) “SENSINGDURATION’)” and subsequently (re)reserve (or select) a V2X messageTX-related resource(s). In another example, if the last ‘repeatedtransmission timing’ (or ‘SF’) (for example, SF#(N+K2)) is designated asthe boundary of a time region in which a sensing operation is performed,the V2X UE performs a sensing operation at the remaining (resource) timepoints except for the (resource) time point at which the V2X UE(actually) performs the V2X message TX operation on the “resource periodranging from SF#(N+K2-D) to SF#(N+K2) (or SF#(N+K2-1-D) to SF#(N+K2-1))”and subsequently (re)reserve (or select) a V2X message TX-relatedresource(s).

(Example#3-2) If part of ‘Q’ repeated transmissions is skipped (orstopped) in an attempt to sense (or measure) a resource used (orreserved (or selected) previously), the first (or last) ‘skipped (orstopped) transmission timing’ (or ‘SF’) may be defined as the boundaryof a time region in which a (resource (re)reservation (orselection)-related) sensing operation is performed.

(Example#3-3) if one V2X message is transmitted ‘Q′ times, the following(partial) parameters may be defined (or managed) differently (orindependently) for each transmission (or for each different REDENDANCYVERSION (RV)’ transmission) (or between the initial transmission andretransmission). Also, in another example, the following (partial)parameters may be defined (or managed) independently (or differently)according to different message ‘sizes (or types)’ and/or ‘transmission(occurrence) periods’ and/or ‘priorities’ (or according to whetherpredefined (or signaled) ‘SECURITY information’ is transmitted togetherwith the parameters). As a specific example, a large value may be set tothe ‘SENSING DURATION’ for a message having a low (or high) priority sothat resource re-reservation (or selection) frequency is made low whilea small value may be set to the ‘SENSING DURATION’ for a message havinga high (or low) priority so that the resource re-reservation (orselection) frequency is made high.

(Example#3-3-1) ‘SENSING DURATION’ (and/or a ‘probability related toperforming resource re-reservation (or selection)’ and/or a ‘backoffvalue related to performing resource re-reservation (or selection)’and/or ‘MAXIMUM RESERVATION TIME’ and/or ‘MUTING (or SILENCING ortransmission skipping (or stopping)) probability (or period orpattern)’.

In a still another example, it may be defined so that a ‘(resource(re)reservation (or selection)-related) sensing operation’ and/or‘resource re-reservation (or selection)’ is performed through thefollowing (partial) rules.

[Proposed Rule#4] When the V2X UE performs a sensing operation on aresource used by the V2X UE (or previously reserved (or selected))according to the “RANDOM MUTING (or SILENCING or transmission skipping(or stopping))” (or “predefined (or signaled) probability-based MUTING(or SILENCING or transmission skipping (or stopping))”), MUTING (orSILENCING) is not applied to all of the SF(s) used for (repeated)transmission of (one) V2X message (or all of the ‘Q’ repeatedtransmissions related to (one) V2X message are not skipped (or stopped))but is applied to only part of the SFs (or repeated transmissions)(periodically) (or only part of the SFs is skipped (or stopped)) in analternate fashion according to a predefined (or signaled) rule (or(hopping) pattern). Here, the corresponding (hopping) pattern may berandomized on the basis of an input parameter(s) such as the ‘(SOURCE)UE ID’ (and/or “period index of a pool (or resource) (with which the V2Xmessage TX operation is performed)’ and/or ‘SA period index’). In a yetanother example, when “(RANDOM) MUTING (or SILENCING or transmissionskipping (or stopping))” is performed, the “(RANDOM) MUTING (orSILENCING or transmission skipping (or stopping)) probability (or periodor pattern)′ may be defined differently (or independently) between theinitial transmission and retransmission. Here, this rule may beinterpreted such that the “(RANDOM) MUTING (or SILENCING or transmissionskipping (or stopping)) probability (or period or pattern)′ is setdifferently (or independently) between ‘RV 0’ (initial transmission) andother ‘RV’ (retransmission) (or it may be interpreted such that the‘(RANDOM) MUTING (or SILENCING or transmission skipping (or stopping))probability (or period or pattern)’ is set differently (orindependently) for each ‘RV’). As a specific example, it may beconfigured so that the “(RANDOM) MUTING (or SLICING or transmissionskipping (or stopping))” is applied to the ‘RV 0’ (initial transmission)with a relatively smaller probability than to other ‘RV’(retransmission).

[Proposed Rule#5] if (one) V2X message is transmitted (repeatedly)through multiple SFs (or if one (V2X) message is transmitted ‘Q’ times),it may be configured so that not all of the SFs (or resources related to‘Q’ repeated transmissions) are re-reserved (or selected) at once butonly predefined (or signaled) ‘T’ SFs (or resources related to repeatedtransmission) are re-reserved (or selected) one by one according to apredefined (or signaled) rule (or (hopping) pattern). Here, the ‘T’value may be set to ‘1’. Also, the corresponding (hopping) pattern maybe randomized on the basis of an input parameter(s) such as the‘(SOURCE) UE ID’ (and/or period index of a pool (or resource) (withwhich the V2X message TX operation is performed)’ and/or ‘SA PERIODindex’). If the rule above is applied, the interference environment maybe prevented from being influenced by an abrupt change due tore-reservation (or selection) of the (whole) resources.

As another example, if (semi-static) (re)reservation (or selection) of aresource(s) related to V2X message TX is performed and a “sensingoperation” is performed through decoding of a predefined (or signaled)channel (for example, PSCCH (or Scheduling Assignment (SA))), ‘DATA (orPhysical Sidelink Shared Channel (PSSCH))’ decoding operation may beperformed according to the following (partial) rule.

[Proposed Rule#6] Suppose the V2X UE succeeds SA (or PSCCH) decoding andresource reservation is set (or on). (A) if SA (or PSCCH) is receivedsuccessfully at the next period, it suffices to perform DATA (or PSSCH)decoding according to the corresponding SA (or PSCCH) (which has beenreceived successfully). (B) (On the other hand) if the V2X UE fails toreceive SA (or PSCCH) at the next period, the V2X UE may be configuredto attempt DATA (or PSSCH) decoding by reusing various kinds ofpredefined (or signaled) information (for example, RESOURCE ALLOCATION(RA), MODULATION AND CODING SCHEME (MCS), and RS SEQUENCE SETTING) ofthe existing (recently received) SA (or PSCCH) (or which has beenreceived most recently).

[Proposed Rule#7] If ‘maximum time’ is defined, which specifies the timeperiod for which (re)reserved (or selected) resources may be maintained(for example, in the case where ‘RESOURCE RESELECTION TIMER’ is defined)or if how long the (re)reserved (or selected) resources are maintainedis specified by the ‘RESERVATION FIELD’ of the PSCCH (or SA) (or on thePSSCH (or DATA)), an RX V2X UE (which has failed to receive SA (orPSCCH)) may be configured to attempt decoding of DATA (or PSSCH) byusing the PSCCH (or SA) which has been received most recently during thecorresponding period and to make the positions of the correspondingresources occupied (by other V2X UE) avoid ‘RESOURCE (RE)ALLOCATION’.

In another example, if a better resource satisfying a predefined (orsignaled) criterion (or rule) is found while the V2X UE already has areserved (or selected) resource, the V2X UE may be made to ‘re-reserve(or select)’ the resource used by the V2X UE (or previously reserved (orselected) resource). In an additional example, to sense (or measure) theresource currently reserved (by the V2X UE), the V2X UE, instead ofperforming ‘MUTING (or SILENCING)’, may move to a predefined (orsignaled), different resource (or pool) for a while (and/or performtransmission of a V2X message (on the corresponding resource (or pool)to which the V2X UE has moved), which may be interpreted as a kind of‘V2X message TX W/O RESERVATION’) and then to perform sensing (ormeasurement) (of the resource that the V2X UE has reserved), returning(back) to the original resource. Here, the ‘time period’ during whichthe V2X UE stays in other resource (or pool) may be predefined (orsignaled). If the rule described above is applied, the ‘MUTING (orSILENCING) operation’ may be used to alleviate the situation wheretransmission of a V2X message is skipped (or stopped).

In a still another example, ‘the boundary of a time region in which aspecific V2X UE performs a sensing operation (related to resource(re)reservation (or selection))’ may be a “PIVOT SF (or REFERENCE SF)”(SF#P) selected on the basis of a predefined (or signaled) rule. Here,when this rule is applied, the V2X UE performs a sensing operation on aresource period ranging from “SF#(P-Y1) to SF#(P+Y2) (here, ‘Y1 =FLOOR((D-1)/2)’ and ‘Y2 = CEILING((D-Y1)2)’ (or ‘Y1 = CEILING((D-1)/2)’and ‘Y2 = FLOOR((D-Y1)/2)’)) (or a resource period ranging from SF#(P-D)to SF#P or a resource period ranging from SF#(P-1-D) to SF#(P-1))” and(re)reserves (or selects) a V2X message TX-related resource(s)afterwards. Here, “D” represents predefined (or signaled) ‘SENSINGDURATION’ and ‘CEILING(X)’ and ‘FLOOR(X)’ represent a ‘functionreturning the minimum integer larger than or equal to X’ and a ‘functionreturning the maximum integer smaller than or equal to X’, respectively.Here, the corresponding “PIVOT SF (or REFERENCE SF)” may be selectedrandomly (on the basis of an input parameter(s) such as ‘(SOURCE) UE ID’(and/or ‘period index of a pool (or resource) period (in which a V2Xmessage TX operation is performed)’ and/or ‘SA PERIOD index’). Also, theproposed rule may be applied limitedly only to the case where (initial)sensing operation is performed after power-up (of the V2X UE) and/or thecase where transmission of a V2X message has never been performed (atall) at the previous time point (or within a (previous) period (orwindow) which lasts a predefined (or signaled) length of time).

In a yet another example, it is assumed that the V2X UE(s) performs ‘SA(or PSCCH)’ transmission related to the ‘DATA (or PSSCH)’ transmissionassociated with the ‘SF#(N+D)’ (for example, D≥C) in the ‘SF#(N+C)’.Here, in one example, when ‘POTENTIAL DATA (or PSSCH)’ transmissionrelated to other TB on the ‘SF#(N+E)’ is performed in the ‘SF#(N+D)’(for example, D < E), the V2X UE may inform of the intent of whether toreuse a ‘(frequency) resource’ (used for ‘DATA (or PSSCH)’ transmissionon the ‘SF#(N+D)’) through a (predefined (or signaled)) channel (forexample, ‘SA (or PSCCH)’ (SF#(N+C)’) (or through ‘DATA (or PSSCH)’).Here, for the convenience of description, the ‘(frequency) resource’indicated (or signaled) as being not ‘intended’ to be reused by the V2XUE#X (when ‘POTENTIAL DATA (or PSSCH)’ transmission related to other TBon the ‘SF#(N+E)’ is performed) is called a ‘UN-BOOKING RESOURCE’. Here,when the V2X UE#Y performs a sensing operation based on ‘ENERGYMEASUREMENT (and/or SA DECODING)’, the ‘(frequency) resource’ indicatedas the ‘UN-BOOKING RESCOURCE’ by the V2X UE#X exhibiting high energy(currently (for example, ‘SF#(N+D)’) or within a sensing period) may beassumed (or processed) according to the following (partial) rule (whenthe V2X UE performs resource selection (or reservation)). This is sobecause, the corresponding ‘(frequency) resource’ indicated as the‘UN-BOOKING RESOURCE’ by the V2X UE#X will not be selected (or reserved)by the V2X UE#Y due to high energy measured (currently (for example,‘SF#(N+D)’) or within a sensing period) even though the corresponding‘(frequency) resource’ may not be used afterwards with a highprobability (for a predetermined time period (including ‘SF#(N+E)’).Here, the following rules may be extended to be applied when the V2XUE(s) informs (other V2X UE(s)) of the fact that the V2X UE(s) makes nofurther use of the resource reserved (or selected) previously (at theresource (re)selection (or reservation) period) (which is also calledthe ‘UN-BOOKING RESOURCE’) from since a particular time point, through apredefined (or signaled) channel (for example, ‘SA (or PSCCH)’ (or ‘DATA(or PSSCH)’)). Here, the following rules may be applied limitedly onlywhen the V2X UE(s) performs a ‘ENERGY MEASUREMENT ONLY′-based sensingoperation or a ‘COMBINATION OF ENERGY MEASUREMENT AND SA DECODING-basedsensing operation (for example, the rules may not be applied when a ‘SADECODING ONLY′-based sensing operation is performed.

[Proposed Rule#8] The V2X UE regards (or assumes) the remainder obtainedby subtracting the ‘RSRP measurement value’ (from the energy valuemeasured on the corresponding ‘(frequency) resource’) (or the remainderobtained by subtracting a predefined (or signaled) offset value) as theenergy measurement value of a ‘(frequency) resource’ designated as the‘UN-BOOKING RESOURCE’ and performs ‘RANKING’ of energy measurementvalues for individual resources. Here, the corresponding ‘RSRPmeasurement’ may be performed on the basis of a reference signal (forexample, ‘DM-RS’) on a predefined (or signaled) channel (for example,‘PSBCH (or ‘PSCCH’ or ‘PSSCH’). Here, if ‘FDM’ is applied to the ‘SA (orPSCCH)’ and ‘DATA (or PSSCH)’, ‘(frequency) resource’ (or ‘SA (orPSCCH)’ or ‘DATA (or PSSCH)’)-related final ‘RSRP (measurement) value’may be finally derived (or assumed) (from the actually measured ‘RSRPvalue’) by compensating (or adding) a (predefined (or signaled)) ‘MPRvalue’ applied (differently) according to a separation distance (on thefrequency region) between ‘SA (or PSCCH) and DATA (or PSSCH)’.

[Proposed Rule#9] The V2X UE may regards (or assume) a predefined (orsignaled) value as the ‘energy measurement value’ or ‘RANKING value’ fora ‘(frequency) resource’ designated as the “UN-BOOKING RESOURCE’. Here,the ‘RANKING’ value for the ‘(frequency) resource’ designated as the‘UN-BOOKING RESOURCE’ may be set (or signaled) as the lowest rank(where, for example, the probability that the corresponding ‘(frequency)resource’ is selected (or reserved) is low) (or as the highest rank(where, for example, the probability that the corresponding ‘(frequency)resource’ is selected (or reserved) is high). In another example, therule may be defined so that at the time of resource selection (orreservation), the ‘(frequency) resource’ designated as the ‘UN-BOOKINGRESOURCE’ is always excluded (or selected (in the first place)).

Meanwhile, the sensing operation of a V2X UE(s) may be performed asfollows.

The proposed methods below describe an (effective) ‘sensing method’ fora V2X UE(s) to select a “V2X message TX-related resource’. Here, if a‘sensing operation’ is applied, different V2X UE(s) (within a closedistance) selects a transmission resource at the same position andthereby alleviates a problem of exchanging interference with each other(when transmission is actually performed) The wording of ‘sensing’ maybe interpreted as (A) an energy (or power) measurement operation and/or(B) a decoding operation for a predefined (or signaled) channel (forexample, Physical Sidelink Control Channel (PSCCH)). Here, the ‘energy(or power) measurement’ may be expressed by (A) Received Signal StrengthIndicator (RSSI) (for example, an average value of received powermeasured from symbols (to which the ‘DM-RS’ of a predefined (orsignaled) antenna port is transmitted or to which data is transmitted)and/or (B) Reference Signal Received Power (RSRP) (for example, anaverage value of received power measured from Resource Elements (REs) towhich the ‘DM-RS’ (of a predefined (or signaled) antenna port) istransmitted) and/or (C) a combination of ‘RSSI’ and ‘RSRP’ according toa predefined (or signaled) rule (or formula) (for example, a formsimilar to the Reference Signal Received Quality (RSRQ)).

In one example, to alleviate (A) the problem that ‘TOPOLOGY’ of a V2XUE(s) is changed, and ‘sensing’ information is made inaccurate and/or(B) the ‘HALF DUPLEX’ problem, (from a viewpoint of a ‘single V2X UE’)‘control (or scheduling) information’ and ‘data (associated with thecorresponding control (or scheduling) information)’ may be transmittedon the same subframe (SF) according to the Frequency DivisionMultiplexing (FDM) scheme.

FIGS. 15 and 16 illustrate one example of a case in which (from aviewpoint of a ‘single V2X UE’) ‘control (or scheduling) information’and ‘data (associated with the corresponding control (or scheduling)information)’ are transmitted on the same SF according to the FrequencyDivision Multiplexing (FDM) scheme

FIGS. 15 and 16 illustrate a ‘case in which control (or scheduling)information and associated data are transmitted on consecutive resourceblocks (RBs)’ and a ‘case in which control (or scheduling) informationand associated data are transmitted on inconsecutive resource blocks(RBs)’. In another example, when ‘LINK BUDGET’ of the ‘control (orscheduling) information’ is considered, (from a viewpoint of a ‘singleV2X UE’) transmitting ‘control (or scheduling) information’ and ‘data(associated with the corresponding control (or scheduling) information’on a different SF according to the Time Division Multiplexing (TDM)scheme may be considered

FIG. 17 illustrates one example of a case in which a ‘control (orscheduling) information transmission pool’ and a ‘data transmissionpool’ are defined (or configured) according to the ‘FDM’ scheme (from asystem point of view).

In one example, (from a system point of view) a ‘control (or scheduling)information transmission pool’ and a ‘data transmission pool’ may bedefined (or configured) according to the ‘FDM’ scheme (A) to satisfy the‘LATENCY REQUIREMENT’ of a ‘V2X SERVICE’ (in an efficient manner) and/or(B) to disperse ‘transmission of control (or scheduling) information’ onthe time domain. FIG. 17 illustrates one example of the aforementionedcase. Here, it is assumed that the ‘data transmission pool’ associatedwith a specific ‘control (or scheduling) information transmission pool’is operated according to the ‘TDM’ scheme.

Meanwhile, although a UE performs sensing in (each) sub-channel (bydefault), actual transmission of a V2X message may be performed in unitsof a plurality of sub-channels. If the UE uses a plurality ofsub-channels used for actual transmission of a V2X message (namely, iftransmission of a V2X message is performed in units of a plurality ofsub-channels), how to perform sensing needs to be taken into account. Inthis respect, in what follows, described will be a method for performingsensing when a plurality of sub-channels is used for transmission of aV2X message.

[Proposed method] In one example, a rule may be defined so that a V2XUE(s) performs a sensing operation in ‘units of resource size’ to beused (by the V2X UE itself) for ‘V2X message TX’. When the correspondingrule is applied, the ‘sensing resource unit size’ of the V2X UE becomesthe same as the ‘resource size’ to be used (by the corresponding V2X UE)for ‘V2X message TX’. For example, when the UE performs energymeasurement through a sensing operation, in which unit or size toperform the energy measurement may have to be considered. At this time,the proposed method according to the present invention may set theresource unit or size used by the UE for data transmission, for example,a sub-channel size, as the unit or size of energy measurement. Forexample, when the UE performs V2X message transmission with a specificsub-channel size, energy measurement for a sensing operation may beperformed in units of resources with the specific sub-channel size. Inwhat follows, the proposed method will be described with reference torelated drawings.

FIG. 18 is a flow diagram illustrating a method for performing sensingwhen multiple sub-channels are used for transmission of a V2X messageaccording to one embodiment of the present invention.

According to FIG. 18 , the UE performs sensing in units of sub-channelthe size of which is equal to the size of a sub-channel used fortransmission of a V2X message, thereby selecting a resource with whichto perform transmission of a V2X message S1810. At this time, the UE mayselect the resource by configuring a selection window within a rangesatisfying the latency requirement, transmission of the V2X message isperformed in units of multiple sub-channels, and a resource with whichto perform the V2X communication may be selected on the basis of thesensing performed in units of sub-channel the size of which is equal tothe size of the plurality of sub-channels. The size of a sensing regionused when the sensing is performed may be equal to the size of theplurality of sub-channels. Moreover, the UE may perform sensing by usingan energy measurement average value of sub-channels belonging to theplurality of sub-channels.

To summarize, when V2X communication is performed in units of multiplesub-channels, the UE may not only perform sensing in units of multiplesub-channels but also select the resource by configuring a selectionwindow within a range that satisfies the latency requirement. Here, anexample of selecting the resource by configuring a selection windowwithin a range that satisfies the latency requirement is the same asdescribed above.

In what follows, described will be an example in which a UE performssensing in units of multiple sub-channels when transmission of a V2Xmessage is performed in units of multiple sub-channels.

The UE may perform sensing in units of sub-channel the size of which isequal to the size of a sub-channel used for transmission of a V2Xmessage and select a resource with which to perform transmission of aV2X message on the basis of the sensing result. In other words, sensing(for example, ENERGY MEASUREMNT) may be performed with a sub-channelsize of data to be transmitted by the UE.

When sensing (for example, ENERGY MEASUREMENT) is performed with thesub-channel size of data to be transmitted by the UE, a linear averagevalue of sub-channels may be used. More specifically, with respect tothe remaining candidate single subframe resources R_(x,y) in the setS_(A) (which is a set of all of the candidate single subframeresources), a sensing region (for example, metric E_(x,y)) may bedefined as a linear average of S-RSSI measured at sub-channels x+k.Here, k is defined as 0, ..., L_(subCH)-1, where L_(subCH) may representthe number of sub-channels required for sending actual packets. For theconvenience of understanding, the present operation may be described asfollows with reference to related drawings.

FIG. 19 illustrates one example in which ENERGY MEASUREMENT (namelysensing) is performed with a sub-channel size of data to be transmittedby the UE. FIG. 19 assumes that the sub-channel size of a V2X message(for example, V2X data) to be transmitted by the UE is 2 (namelyL_(subCH) = 2).

In the example of FIG. 19 , ENERGY MEASUREMENT may be performed in unitsof two sub-channels corresponding to the sub-channel size of datatransmitted by the UE. First, the UE may determine a sensing value withrespect to the sensing region#1 by using the average of energy sensingvalues with respect to the sensing region#1, namely sub-channel#1 andsub-channel#2. Moreover, the UE may determine a sensing value withrespect to the sensing region#2 by using the average of energy sensingvalues with respect to the sensing region#2, namely sub-channel#2 andsub-channel#3. In the same way, the UE may determine a sensing valuewith respect to the sensing region#3 by using the average of energysensing values with respect to the sensing region#3, namelysub-channel#3 and sub-channel#4.

Although FIG. 19 assumes that the sub-channel size of data to betransmitted by the UE is 2, the sub-channel size of data to betransmitted by the UE may have a value of 3 or more. Although not shownin a separate figure, if the sub-channel size of data to be transmittedby the UE is 3, the UE may determine the sensing value with respect to asensing region by using the average of energy sensing values in thesub-channel#1 to sub-channel#3.

Referring again to FIG. 18 , the UE may transmit a V2X message by usingthe selected resource S1820. As described above (or below), the UE mayselect a subframe within a selection window on the basis of a sensingresult obtained by performing sensing during a UE-specific sensingperiod, determine transmission reservation resources on the basis of aselected subframe, and perform V2X communication on the reservedresource Since a specific example in which a UE performs V2Xcommunication on the basis of a selected resource is the same asdescribed above (or below), detailed descriptions thereof will beomitted.

FIGS. 20 and 21 illustrate one example of ‘PARTIALLY OVERLAPPED REGIONBASED SENSING’ (or ‘SLIDING WINDOW BASED SENSING’).

In one example, a sensing operation may be implemented in the form of(A) ‘NON-OVERLAPPED REGION BASED SENSING’ (see FIG. 20 ) and/or (B)‘PARTIALLY OVERLAPPED REGION BASED SENSING’ (or ‘SLIDING WINDOW BASEDSENSING’) (see FIG. 21 ). When the former rule (‘(A)’) is applied,sensing regions in which a sensing operation is performed (continuously)do not overlap with each other (for example, it may be seen from FIG. 20that ‘(sensing region#1)’, ‘(sensing region#2)’, and ‘(sensingregion#3)’ are not overlapped). (On the other hand) when the latter rule(‘(B)’) is applied, for example, sensing regions in which a sensingoperation is performed (continuously) overlap with each other by apredefined (or signaled) ‘ratio’ (or ‘amount of resources (or size)’)(for example, FIG. 21 shows that ‘(sensing region#1) and (sensingregion#2)’, ‘(sensing region#2) and (sensing region#3)’, ‘(sensingregion#3) and (sensing region#4)’, and ‘(sensing region#4) and (sensingregion#5)’ are overlapped with each other by a predefined (or signaled)‘ratio’ (or ‘amount of resources (or size)’). In one example, the formerrule (‘(A)’) may reduce the ‘complexity in performing a sensingoperation’ compared with the latter rule (‘(B)’). In other words,compared with the latter rule (‘(B)’), ‘the total number of sensing’required for a resource pool of the same size may be relatively smallwhen the former rule (‘(A)’) is employed. On the other hand, when thelatter rule (‘(B)’) is employed, (although ‘the total number of sensing’required for a resource pool of the same size may be larger than thatwhen the former rule (‘(A)’) is employed,) the ‘position of an availableresource candidate′-related to ‘V2X message TX’ may be searched (orselected) in a relatively efficient (or outright) manner.

As another example, the V2X UE may be made to perform a sensingoperation (first) with a predefined (or signaled) ‘resource unit (size)’(for example, ‘1 RB’), and a ‘(weighted) average value’ (or ‘SUM’) of aplurality of sensing (or measurement) values corresponding to the‘resource size (or unit)’ to be used for ‘V2X message TX’ (or themaximum value (or minimum value or median value) among a plurality ofsensing (or measurement) values) may be regarded (or assumed) as arepresentative sensing (or measurement) value for each ‘resource size(or unit)’ (to be used for ‘V2X message TX’).

As a still another example, when the V2X UE(s) performs ‘(V2X) channelor signal transmission (for example, ‘MULTI-CLUSTER TX’ (or ‘DVRB TX’))by using (a plurality of) resources at ‘discontinuous positions’ on the‘frequency (resource) region’, the V2X UE(s) may be made to perform asensing (or measurement) operation with a predefined (or signaled)‘sensing resource unit (or size)’ (for example, in units of K RBs) (orperform ‘NON-OVERLAPPED REGION BASED SENSING’ or ‘PARTIALLY OVERLAPPEDREGION BASED SENSING’ (or ‘SLIDING WINDOW BASED SENSING’) in units ofRESOURCE BLOCK GROUPs (RBGs)), and to (finally) select ‘V2X messageTX′-related resources (among resources of which the (energy) measurementis smaller (or larger) than a predefined (or signaled) threshold value).

In another example, it is assumed that, to transmit a ‘(SINGLE) V2X TB(or message)’, the V2X UE(s) performs ‘K’ repeated transmissions (forexample, the ‘K’ value includes (both of) the number of ‘initialtransmissions’ and the number of ‘retransmissions’). Here, for theconvenience of description, ‘K’ value is set to ‘4’. Now let’s assumethat ‘SA (or PSCCH)’ transmission is performed in the ‘SF#(N+C)’, andassociated (four) ‘DATA (or PSSCH)’ transmissions are performed in the‘SF#(N+D)’, ‘SF#(N+D+K1)’, ‘SF#(N+D+K2)’, and ‘SF#(N+D+K3)’,respectively (for example, C ≤ D, 0 < K1 < K2 < K3). Here, a field forinforming of ‘positions of time resources’ related to (A) ‘K’ or (B)‘(K-1)’ repeated transmissions may be defined on the ‘SA (or PSCCH)’(‘SF#(N+C)’), and to this end, the following (partial) rules may beapplied In the latter case (‘(B)’), the corresponding field may beinterpreted to inform of the ‘time resource positions’ related to the‘remaining (‘(K-1)’) transmissions except for the ‘initial (or first)transmission’ and/or the ‘initial (or first) transmission’ isinterpreted to be performed (always) at the same time resource(position) as the ‘SA (or PSCCH)’ (‘SF#(N+C)’) and/or the ‘time resourceposition’ related to the ‘initial (or first) transmission’ is signaledto (other) field which informs of the interval between the transmissiontime of ‘SA (or PSCCH)’ (‘SF#(N+C)’) and the ‘initial (or first)transmission’ time.

(Example#A) The ‘time resource position’ related to the ‘initial (orfirst) transmission’ is signaled to (other) ‘FIELD#F’ which informs ofthe interval between the (predefined) ‘SA (or PSCCH)’ (‘SF#(N+C)’)transmission time and the ‘initial (or first)’ time (‘SF#(N+D)’), andthe ‘time resource positions’ related to the ‘remaining (‘(K-1)′)transmissions’ (for example, ‘SF#(N+D+K1)’, ‘SF#(N+D+K2)’, and‘SF#(N+D+K3)’) may be signaled to a (new) ‘FIELD#S’ having the same sizeas the maximum interval (MAX_GAP) between the predefined (or signaled)‘first transmission’ (‘SF#(N+D)’) time and the ‘K-th transmission’(‘SF#(N+D+K3)’) time. Here, the ‘FIELD#S’ may be implemented in the formof a ‘bitmap’. The ‘FIELD#S’ related ‘bitmap’ may be applied by usingthe ‘initial (or first) (DATA (or PSSCH)) transmission’ (‘SF#(N+D)’)time as a reference (or start point). If the ‘MAX_GAP’ is set (orsignaled) to ‘10’, the ‘FIELD#S’ is signaled (or set) to ‘10’, and the‘FIELD#S’ is signaled (or set) to ‘0100100100’, the ‘secondtransmission’, ‘third transmission’, and ‘fourth transmission’ areperformed on the ‘SF#(N+D+2)’, ‘SF#(N+D+5)’, and ‘SF#(N+D+8)’,respectively. As another example, the ‘time resource positions’ relatedto ‘K’ repeated transmissions (for example, ‘SF#(N+D)’, ‘SF#(N+D+K1)’,‘SF#(N+D+K2)’, and ‘SF#(N+D+K3)’ may be signaled to a (new) ‘FIELD#Q’having the same size as the maximum interval (MAX_TVAL) between thepredefined (or signaled) ‘SA (or PSCCH)’ (‘SF#(N+C)’) transmission timeand the ‘K-th transmission’ (‘SF#(N+D+K3)’) time. Here, the ‘FIELD#Q’may be implemented in the form of a ‘bitmap’. The ‘FIELD#Q’ related‘bitmap’ may be applied by using the ‘SA (or PSCCH)’ (‘SF#(N+C)’) timeas a reference (or start point). If the ‘MAX_TVAL’ is set (or signaled)to ‘10’, and the ‘FIELD#Q’ is signaled (or set) to ‘1100100100’, the‘first transmission’, ‘second transmission’, ‘third transmission’, and‘fourth transmission’ are performed on the ‘SF#(N+C+1)’, ‘SF#(N+C+2)’,‘SF#(N+C+5)’, and ‘SF#(N+C+8)’, respectively. In the correspondingexample, if the ‘FIELD#F’ is defined on the ‘SA (or PSCCH)’(‘SF#(N+C)’), the ‘FIELD#F’ value may be set to 1. As another example,due to V2X communication-related ‘CONGESTION (or LOAD or MEASUREMENT)CONTROL, the ‘pattern (form or number of items)’ (or ‘(maximum (orminimum)) value (or length)’) that the ‘FIELD#S’ (or ‘FIELD#Q’ (or‘FIELD#F’)) may have or ‘the number of (maximum (or minimum)) bits thatmay be set to ‘1’ (on the bitmap)’ may be limited. Here, thecorresponding (limited) information may be determined by the V2X UE(s)after examining the ‘CONGESTION (or LOAD or MEASUREMENT)’ situation(according to a predefined (or signaled) rule (or criterion)) or set (orsignaled) by a (serving) base station (on the basis of the ‘CONGESTION(or LOAD or MEASUREMENT)’ information reported by the V2X UE(s) ormeasured by the (serving) base station . Here, due to the V2Xcommunication-related ‘CONGESTION (or LOAD or MEASUREMENT)’, the‘MAX_GAP’ (or the ‘maximum (or minimum) value (or length)’ that‘MAX_TVAL’ may have) may (also) be limited.

(Example#B) The ‘time resource positions’ related to ‘K’ repeatedtransmissions (for example, ‘SF#(N+D)’, ‘SF#(N+D+K1)’, ‘SF#(N+D+K2)’,and ‘SF#(N+D+K3)’) may be signaled to ‘K’ ‘FIELD#F’s defined on the ‘SA(or PSCCH)’ (‘SF#(N+C)’) (‘(Example#A)’) (for example, the ‘(X-th)FIELD#F’ informs of the interval (in the time region) between the ‘SA(or PSCCH)’ (‘SF#(N+C)’) transmission time and ‘X-th transmission’time).

(Example#C) (In a situation where the (partial) rules (for example,(Example#A) and (Example#B)) are applied) if ‘SA (or PSCCH)’transmission is performed each time ‘DATA (or PSSCH)’ is transmitted(‘K’ times (for example, ‘SF#(N+D)’, ‘SF#(N+D+K1)’, ‘SF#(N+D+K2)’, and‘SF#(N+D+K3)’), the following (partial) rule may be applied. Here, thefollowing (partial) rules may be applied limitedly only to the casewhere ‘(DATA (or PSSCH)) FREQUENCY HOPPING’ is performed.

(Example#1) ‘SF PATTERN’ information (or field) on the ‘SA (or PSCCH)’(‘SF#(N+C)’) related to the ‘initial (or first) transmission’(‘SF#(N+D)’) and/or ‘frequency resource (position)’ information (orfield) and/or part of the ‘MCS’ information (or field) may also betransmitted on the ‘remaining (‘(K-1)’) transmission′-related ‘SA (orPSCCH)’ in the same manner. To distinguish the aforementioned operation,if one ‘TB’ is transmitted from multiple SFs, ‘COUNTER’ informationindicating the corresponding ((DATA (or PSSCH) transmission) SF (orinformation (or field) about to which transmission the ‘DATA (or PSCCH)transmission’ corresponds or ‘RV’ information (or field) related to‘DATA (or PSCCH) transmission’) may be included in the ‘SA (or PSCCH)’which schedules (DATA (or PSSCH)) transmission on each SF. Here, the‘initial (or first) transmission’ (‘SF#(N+D)’)-related ‘SA (or PSCCH)’(‘SF#(N+C)’) may define (at least) ‘initial (or first) transmission’related ‘frequency resource (position)’ information (or field) and/or‘MCS’ information (or field) and/or (the aforementioned) ‘FIELD#S’ (or‘FIELD#Q’) (or ‘SF PATTERN’ information (or field)) and/or ‘FIELD#F’(which, for example, may be (further) interpreted as a field informingof the interval between the ‘X-th transmission’ related ‘SA (or PSCCH)’transmission time and the ‘X-th transmission’ time) and/or information(or field) about which transmission is the ‘(cor-responding) DATA (orPSCCH) transmission’ (or ‘(corresponding) DATA (or PSCCH) transmission’related ‘RV’ information (or field)) (and/or information (or field)about whether ‘(DATA (or PSSCH)) FREQUENCY HOPPING’ has been applied).If the corresponding rule is applied, ‘frequency resource (position)’information related to the ‘remaining (K-1) transmissions’ may not be(directly) transmitted (or signaled) on a related ‘SA (or PSCCH)’ and/or‘FIELD#F’ values are set to the interval between the ‘initial (or first)transmission’ related ‘SA (or PSCCH)’ transmission time and the ‘initial(or first) transmission’ time, however, even if the V2X UE(s) fails toreceive (or decode) ‘previous transmission′-related ‘SA (or PSCCH)’,once the V2X UE(s) succeeds to received (or decode) ‘subsequenttransmission′-related ‘SA (or PSCCH)’, the corresponding ‘subsequenttransmission’ related ‘frequency resource (position) information’ may befound (or derived) (in the form of backtracking) by combining (A) ‘(DATA(or PSSCH)) FREQUENCY HOPPING pattern’ information and/or (B) ‘initial(or first) transmission’ related ‘frequency resource (position)’information on the ‘subsequent transmission’-related ‘SA (or PSCCH)’and/or (C) ‘FIELD#S’ (or ‘FIELD#Q’) information (or ‘SF PATTERN’information) and/or information about which transmission is the ‘DATA(or PSCCH) transmission’ (or ‘DATA (or PSCCH) transmission′-related ‘RV’information). Here, the ‘subsequent transmission’ related ‘time resource(position) information’ may be figured out (or derived) through the‘FIELD#F’ on the ‘subsequent transmission ‘SA (or PSCCH)’. Here, whenthe proposed rule is applied, (in particular, when the ‘(DATA (orPSSCH)) FREQUENCY HOPPING’ operation is applied,) a V2X UE(s) which hassucceeded to receive (or decode) the ‘initial (or first)transmission′-related ‘SA (or PSCCH)’ may not attempt to decode (orreceive) (part of) the ‘remaining (‘(K-1)’) transmission′-related ‘SA(or PSCCH)’. As another example, (from the proposed rule,) ‘FIELD#F’(which, for example, may be interpreted as ‘TIMING GAP’ between the ‘SA(or PSCCH)’ transmission time and the ‘associated DATA (or PSSCH)’transmission time) (or a field informing of the ‘intent’ of whether toreuse ‘(frequency) resource’ employed for previous ‘DATA (or PSSCH)’transmission when other ‘TB’ related ‘POTENTIAL DATA (or PSSCH)’transmission is performed afterwards (at particular time)) may bedefined (or signaled) independently at each ‘SA (or PSCCH)’ transmission(or in the same manner (for all ‘SA (or PSCCH)’ transmission)). Here,when the corresponding rule is applied, the V2X UE(s) may be made toattempt to decode (or receive) (all of the ‘K’ transmissions) withrespect to the ‘K’ transmission-related ‘SA (or PSCCH)’. In a yetanother example, (from the proposed rule) (when one ‘TB’ is transmittedfrom multiple SFs,) a V2X TX UE may perform ‘RESOURCE RESELCTION’operation (in the middle of operation) according to a predefined (orsignaled) rule (which includes, for example, a case where ‘SA (orPSCCH)’ (or ‘DATA (or PSSCH)’) having a ‘HIGHER PRIORITY’ transmitted byother V2X UE(s) is detected and a case where ‘CURRENT RESOURCEALLOCATION’ does not satisfy the predefined (or signaled) ‘REQIJIREMENT’(for example, LATENCY, RELIABILITY, PRIORITY, FAIRNESS, and QoS)).Therefore, the V2X RX UE may be made to follow the ‘subsequent SA(PSSCH)’ when (the corresponding ‘TB’ related) ‘subsequent SA (orPSSCH)’ performs scheduling different from the ‘previous SA (or PSCCH)’

(Example#2) (In the (Example#1),) when ‘SA (or PSCCH)’ related to the‘X-th transmission’ (for example, ‘X > 1’) is transmitted, ‘FIELD#S’ (or‘FIELD#Q’) may be configured by regarding the corresponding ‘X-thtransmission’ as if the ‘initial (or first) transmission’. In anotherexample, when ‘frequency resource (position)’ information (or field) isdefined on the ‘SA (or PSCCH)’ and ‘(DATA (or PSSCH)) FREQUENCY HOPPING’operation is performed, the ‘frequency resource (position)’ information(or field) value itself may be set differently for each ‘SA (or PSCCH)’transmission (by taking into account the ‘(DATA (or PSSCH)) FREQUENYHOPPING pattern’). This is so because, after ‘(DATA (or PSSCH))FREQUENCY HOPPING’ is applied to the ‘frequency resource (position)’scheduled by the ‘N-th transmission′-related ‘SA (or PSCCH)’, the‘(N+1)-th transmission′-related ‘SA (or PSCCH)’ has to designate (orsignal) the (corresponding) changed ‘frequency resource (position)’.

In a yet another example, the V2X UE(s) may be made to reselect a(transmission) resource reserved (or selected) by the V2X UE(s) (duringa predetermined period of time (or repetition period)) each time apredefined (or signaled) condition is met. Here, the V2X UE(s) may bemade to select a COUNTER value from a predefined (or signaled) range(“C_RANGE”) and if the corresponding counter becomes ‘0’ (or a valuesmaller than ‘0’), to reselect the (transmission) resource reserved (orselected) by the V2X UE(s) (during a predetermined period of time (orrepetition period)) Here, the corresponding counter may be (A) reduced(or increased) to a predefined (or signaled) value (for example, ‘1’)for each (new) TB transmission (for example, ‘TB transmission’ may beinterpreted to indicate only ‘actually (successfully) performed TBtransmission’ and/or (due to a ‘sensing result’ and/or ‘collision withtransmission of a message (of other V2X UE(s)) having a relatively highpriority,) the ‘TB transmission’ may be interpreted to include ‘skippedTB transmission’) or (B) reduced (or increased) to a predefined (orsignaled) value (for example, ‘1’) every predefined (or signaled)(period) values (for example, ‘100 ms’). Here, an operation of(re)selecting a counter value from a predefined (or signaled) range (oran operation ‘RESETTING’ the counter value) may be defined as a case inwhich ‘(ALL) SEMI-PERSISTENTLY SELECTED RESOURCE(S)′-related‘(RESOURCE(S)) RESELECTION’ has been triggered. Here, the ‘C __RANGE’value may be set (or assumed) (partly) differently according to thefollowing (partial) parameters. The ‘C_RANGE’ value (according to therange of a (specific) parameter) may be predefined or signaled from thenetwork.

(Example#l) ‘V2X UE VELOCITY’. In the case of fast ‘V2X UE VELOCITY’(which is relatively fast or faster than a predefined (or signaled)threshold value), a (relatively) long (or short) ‘C_RANGE’ value may beapplied.

(Example#2) ‘(TRANSMISSION) SYNCHRONIZATION REFERENCE TYPE’ (forexample, ‘eNB’, ‘GNSS’, ‘UE’). Here, when ‘(TRANSMISSION)SYNCHRONIZATION REFERENCE TYPE’ is GNSS (or eNB or UE), a (relatively)long (or short) ‘C_RANGE’ value may be applied. (The ‘C_RANGE’ value is(relatively) long (or short) compared with the case in which‘(TRANSMISSION) SYNCHRONIZATION REFERENCE TYPE’ is eNB (or UE or GNSS).)

(Example#3) ‘V2X MESSAGE TRANSMISSION (and/or GENERATION) PERIODICITY’.In the case of long ‘V2X MESSAGE TRANSMISSION (and/or GENERATION)PERIODICITY’ (which is relatively long or longer than a predefined (orsignaled) threshold value), a (relatively) long (or short) ‘C₋RANGE’value may be applied.

(Example#4) ‘V2X MESSAGE (and/or SERVICE) TYPE’ (for example,‘EVENT-TRIGGERED MESSAGE’, ‘PERIODIC MESSAGE’ (or a ‘message with(relatively) small LATENCY REQUIREMENT (and/or (relatively) highreliability (or QoS) REQUIREMENT and/or (relatively) high priority’), ‘amessage with (relatively) long LATENCY REQUIREMENT (and/or (relatively)low reliability (or QoS) REQUIREMENT and/or (relatively) low priority’).Here, in the case of’EVENT-TRIGGERED MESSAGE’, a (relatively) long (orshort) ‘C_ RANGE’ value may be applied. (The ‘C_RANGE’ value is(relatively) long (or short) compared with the case of ‘PERIODICMESSAGE’.)

(Example#5) ‘V2X MESSAGE (and/or SERVICE) PRIORITY (and/or LATENCYREQUIREMENT and/or RELIABILITY REQUIREMENT and/or QoS REQUIREMENT).Here, in the case of (relatively) low ‘V2X MESSAGE (and/or SERVICE)PRIORITY (and/or LATENCY REQUIREMENT and/or RELIABILITY REQUIREMENTand/or QoS REQUIREMENT)’, a (relatively) long (or short) ‘C_RANGE’ valuemay be applied.

In another example, a V2X TX UE(s) may be made to perform a (V2Xmessage) transmission resource (re)reservation (or selection) operationaccording to the following (all or part of) rules. The (corresponding)transmission resource (re)reservation (or selection) operation may be(at least) triggered when the (transmission resource (re)reservation)counter value (SEL_CNTVAL) selected randomly within a predefined (orsignaled) range (for example, “5 -15”) by the V2X TX UE(s) becomes “0”(and/or a “negative integer value”). In one example, after it isregarded (or assumed) that for each (actual) transmission of a TransportBlock (TB) (or packet) (and/or irrespective of (actual) TB (or packet)transmission), as many transmission resources (having a resourcereservation (interval) period “P”) as the (selected) counter value(and/or the value derived from the (selected) counter value) have beenreserved (or selected), the (selected) counter value may be made to bereduced by a predefined (or signaled) value (for example, “1”) each timethe corresponding reserved (or selected) transmission resource is passed(on the time region) and/or if a TB (or packet) (to be transmitted orgenerated (or received)) on a (LOW LAYER) buffer (and/or PDCP LAYER)exists (and/or does not exist). In the present invention, the term“(re)reservation (or selection)” may be (generally) interpreted as (A)re-reserving (or selecting) a transmission resource (different from (orthe same as) the existing resource) on the basis of a sensing resultwhen the V2X TX UE(s) determines not to maintain (or reuse) a(transmission) resource selected previously on the basis of a(predefined (or signaled)) probability value (KEEP_P) (for example, the“aforementioned STEP 3”) (for example, it is assumed that a previouslyselected (transmission) resource is maintained only when a valueselected randomly between 0 and 1 is less than or equal to the KEEP_P)(or irrespective of the corresponding probability value (KEEP_P)) and/or(B) the V2X TX UE(s)’s maintaining (or reusing) a (transmission)resource selected previously on the basis of a (predefined (orsignaled)) probability value (KEEP _P) (or irrespective of thecorresponding probability value (KEEP_P)) and/or (C) reserving (orselecting) (again) a finite number (or a predefined (or signaled)(other) number (which, for example, is interpreted to be larger than (orlarger than or equal to) SEL_CNTVAL value (and/or a value derived fromthe SEL_CNTVAL value)) of subframes which are the same as existingsubframes (or the same resources (as the existing ones)). If the‘(re)reservation (or selection)’ operation is performed (in general),the (transmission resource (re)reservation) counter value may be made tobe selected (randomly) (or (instead of newly (randomly) selecting thecounter value), the (transmission resource (re)reservation) countervalue may use (or maintain or apply) an existing value (SEL_CNTVAL) (orthe remaining value (or a predefined (or signaled) (other) value)).

(Example#1) When the V2X TX UE(s) performs transmission resource(re)reservation (or selection), after the V2X TX UE(s) (first) reserves(or selects) an infinite number of subframes (or resources) (having aresource reservation (interval) period “P”), the V2X TX UE(s) may bemade to use the (corresponding) reserved (or selected) resources untilthe transmission resource (re)reservation (or selection) operation istriggered. However, if the corresponding rule is applied, a “SYSTEMFRAME NUMBER (SFN) WRAP AROUND” problem may occur.

In what follows, for the convenience of understanding, a situation inwhich the “SYSTEM FRAME NUMBER (SFN) WRAP AROUND” problem occurs will bedescribed with reference to related drawings.

FIG. 22 illustrates a situation in which the “SYSTEM FRAME NUMBER (SFN)WRAP AROUND” problem occurs.

FIG. 22 assumes that a V2X TX UE#X attempts to perform transmissionresource (re)reservation (or selection) with a resource reservation(interval) period of “100 ms” at SUBFRAME#0 time point. It is furtherassumed that all of 1024 subframes are set (or signaled) as a V2Xresource (pool). In this case, when the V2X TX UE#X needs to selectSUBFRAM E#0, SUBFRAME#100, ..., SUBFRAME#10200, and SUBFRAME#10300, theV2X TX UE#X selects SUBFRAME#60 (due to the constraint on the SFN). As aresult, when the V2X TX UE#X finishes selecting (all of) the subframes,a second transmission opportunity comes before the SUBFRAME#100.

Meanwhile, to solve the corresponding problem, the V2X TX UE(s) may bemade to (first) reserve (or select) a finite number (FINI_SFNUM) ofsubframes (or resources) (having a resource reservation (interval)period “P”) when transmission resource (re)reservation (or selection) isperformed. In what follows, an example in which a UE reserves a finitenumber of resources (namely 10*SL_RESOURCE_RESELECTION_COUNTER)according to a predefined rule will be described with reference torelated drawings.

FIG. 23 is a flow diagram illustrating a method for reserving a finitenumber of resources according to one embodiment of the presentinvention.

Referring to FIG. 23 , the UE may perform reservation of a finite numberof resources by which V2X communication is performed S2310. The UE mayselect a resource on a selection window and perform reservation ofrepeated resources on the basis of a specific period by using theselected resource, where the number of reserved resource(s) is finite.At this time, the finite number may be proportional to a counter value(for example, SL_RESOURCE_RESELECTION_COUNTER) selected (or determined)randomly, where the counter value may have a positive integer. Moreover,the finite number may have a value ten times the counter value selectedrandomly by the UE. In what follows, an example where the UE reserves afinite number of resources will be descried in detail.

The UE may reserve a plurality of resources with which V2X communicationis performed, and the number of reserved resources may be finite. Whenthe UE reserves a finite number of resources, a predefined rule (forexample, 10 * SL_RESOURCE_RESELECTION_COUNTER) may be applied.

As a specific example of a predefined rule, the number of subframes inone set of time and frequency resource with respect to the transmissionopportunity of PSSCH may be set to a specific value (for example,C_(resel)). At this time, Cresel may be defined as10*SL_RESOURCE_RESELECTlON_COUNTER (when a specific counter (forexample, SLRESOURCE_RESELECTION_COUNTER) is configured), otherwise(namely when SL_ RESOURCE_RESELECTION_COUNTER has not been configured),C_(resel) may be set to 1. Here, SL_RESOURCE_RESELECTION_COUNTER may beset to a random value of 5 or more and 15 or less.

For example, when SL_RESOURCE_RESELECTION_COUNTER is 5, a total of 50subframes may be reserved for transmission of PSSCH while, when SL_RESOURCE_RESELECTION_COUNTER is 15, a total of 150 subframes may bereserved for transmission of PSSCH.

The (corresponding) finite number may be defined by (A) the total number(TNUM_V2XSF) of subframes (or resources) set (or signaled) as a V2Xresource (pool) (where TNUM­_V2XSF value may be interpreted to be apositive integer of 10240 or less (including ‘0’)) (or “FLOOR(TNUM_V2XSF/resource reservation (interval) period (P))” (or “CEILING(TNUM_V2XSF/resource reservation (interval) period (P))” or “FLOOR(10240/resource reservation (interval) period (P))” or “CEILING(10240/resource reservation (interval) period (P))”) (where FLOOR(X) andCEILING(X) represent a function returning the greatest integer less thanor equal to X and a function returning the least integer greater than orequal to X, respectively) or (a value less than (or less than or equalto) (predefined (or signaled)) TNUM_V2XSF (or 10240)) and/or (B) a(specific) value (predefined (or signaled) by a (serving) eNB (or fromthe network)). Here, the (corresponding) finite number (and/orTNUM_V2XSF value) may be interpreted to be larger (or larger than orequal to) than SEL_CNTVAL value (and/or a value derived from theSEL_CNTVAL value) (and/or the (corresponding) finite number (and/orTNUM_V2XSF value) may be interpreted as the maximum number of subframes(or resources) (of a kind) that may be reserved (or selected)). Byapplying the corresponding rule, the problem that (all of) the reserved(or selected) subframes (or resources) are passed (in the time region)even though the (selected) counter value is a positive integer may alsobe alleviated. Here, although the V2X TX UE(s) defines the(corresponding) finite number (which, for example, may be interpreted asthe maximum number of subframes (or resources) (of a kind) that may bereserved (or selected)), if the SEL_CNTVAL value (and/or a value derivedfrom the SEL_CNTVAL value) is less than the (corresponding) finitenumber, the V2X TX UE(s) may be made to (exceptionally) reserve (orselect) SEL_CNTVAL (and/or a value derived from the SEL_CNTVAL valueand/or a value smaller than the SEL_CNTVAL) subframes (or resources).

The UE may perform V2X communication on the finite number of resourcesS2320. The UE performs V2X communication on a reserved resource in thesame way as described above.

Meanwhile, the UE does not perform V2X transmission indefinitely on areserved resource. In other words, the UE may reselect a reservedtransmission resource, and as described above, the (corresponding)transmission resource (re)reservation (or selection) operation may betriggered (at least) when the (transmission resource (re)reservation)counter value (SEL_CNTVAL) selected randomly within a predefined (orsignaled) range (for example, “5 -15”) by the V2X TX UE(s) becomes 0(and/or a “negative integer value”).

At this time, when there is no more reserved resource lest, the V2X UEmay perform resource reselection on in a selection window. Also, whenthe V2X UE does not perform V2X transmission for 1 continuous second,resource reselection may be performed in the selection window while,when the V2X UE does not perform V2X transmission continuously for apredetermined number of transmission opportunities, resource reselectionmay be performed in the selection window. In one example, while the(corresponding) finite number (and/or TNUM_V2XSF) of reserved (orselected) subframes (or resources) are (all) passed (in the time region)(and/or a predefined (or signaled) subframe index (for example, 10240(or TNUM_V2XSF) passes), if the (selected) counter value does not become“0” (and/or a “negative integer value”), the V2X TX UE(s) may be made toperform the transmission (re)reservation (or selection) operation but tonewly (randomly) select a (transmission resource (re)reservation)counter value (or (instead of newly (randomly) selecting a (transmissionresource (re)reservation) counter value), an existing value (SEL_CNTVAL)(or the remaining value (or predefined (or signaled) (other) value)) maybe used (or maintained or applied).

A specific example in which a UE reselects a transmission resource willbe described later.

The (corresponding) term “transmission resource (re)reservation (orselection) operation” may be interpreted as (A) (re)reserving (orselecting) a transmission resource (different from (or the same as) theexisting resource) on the basis of a sensing result when the V2X TXUE(s) determines not to maintain (or reuse) a (transmission) resourceselected previously on the basis of a (predefined (or signaled))probability value (KEEP_P) (or irrespective of the correspondingprobability value (KEEP_P)) and/or (B) the V2X TX UE(s)’s maintaining(or reusing) a (transmission) resource selected previously on the basisof a (predefined (or signaled)) probability value (KEEP_P) (orirrespective of the corresponding probability value (KEEP_P)) and/or (C)reserving (or selecting) (again) a finite number (or a predefined (orsignaled) (other) number (which, for example, is interpreted to belarger than (or larger than or equal to) SEL_CNTVAL value (and/or avalue derived from the SEL_CNTVAL value)) of subframes which are thesame as existing subframes (or the same resources (as the existingones)).

(Example#2) (When (Example#1) is applied) a V2X TX UE#X (for example,resource reservation (interval) period “P_X”) may be made to determine(for example, the aforementioned “STEP 2”) whether a transmissionresource having a resource reservation (interval) period “P_Y” reserved(or selected) by other V2X TX UE#Y collide (or is overlapped) with acandidate resource that may be reserved (or selected) by the V2X TX UE#Xaccording to whether collision (or overlap) occurs when the (finite)number (NUM_EXTX) of transmissions assumed (or considered) by the V2X TXUE#X is assumed (or considered) to be performed (on the correspondingcandidate resource) (or when it is assumed (or considered) thattransmission is performed as many times as the finite number ofsubframes (or resources) (having a resource reservation (interval)period “P_X”) reserved (or selected) by the V2X TX UE#X). Here, in oneexample (of a case in which the corresponding rule is applied), if it isfound (from (SUBFRAME#(N-10)) PSCCH decoding) that the V2X TX UE#Y(having a resource reservation (interval) period of “100 ms”) hasreserved (or selected) a transmission resource on the SUBFRAME#(N-10)and SUBFRAME#(N+990) with a resource reservation (interval) period of“1000 ms”, the V2X TX UE#X may be made to perform monitoring“SUBFRAME#(N+90), SUBFRAME#(N+190), SUBFRAME#(N+290), SUBFRAME#(N+390),SUBFRAME#(N+490), SUBFRAME#(N+590), SUBFRAME#(N+690), SUBFRAME#(N+790),SUBFRAME#(N+890) (, SUBFRAME#(N+990))” (and/or“SUBFRAME#(N+(990-100*9)), SUBFRAME#(N+(990-100*8)),SUBFRAME#(N+(990-100*7)), SUBFRAME#(N′(990-100*6)),SUBFRAME#(N+(990-100*5)), SUBFRAME#(N+(990-100*4)),SUBFRAME#(N+(990-l00*3)), SUBFRAME#(N+(990-100*2)),SUBFRAME#(N+(990-100)) (,SUBFRAME#(N+990))”) to determine whether acandidate resource (at the same (frequency) position as the V2X TX UE#Y)may be selected on the SUBFRAME#(N+90) (within a predefined (or assumed)“(TX RESOURCE) SELECTION WINDOW”) when transmission resource(re)reservation (or selection) is performed at the SUBFRAME#N (currenttime). The corresponding monitoring performed by the V2XTX LTE#X maydetermine whether a candidate resource (SUBFRAME#Z (for example, “Z =(N+90)”) at the same (frequency) position reserved (or selected) by theV2X TX UE#Y (within the predefined (or assumed) “(TX RESOURCE) SELECTIONWINDOW”) is selectable from whether the time point (for example,SUBFRAME#G (for example, “G = (N+990)”)) (which, for example, may beinterpreted as a kind of “UPPER BOUND”) of a resource (or subframe)reserved (or selected) by the (corresponding) V2X TX UE#Y (on the basisof “P_Y”) (additionally) is overlapped with SUBFRAME#(Z+P__X*K) (here,for example, “0 ≤ K ≤ (the greatest (integer) M value satisfying acondition that “(Z+P_X*M)” value is less than or equal to “G″ value”)(and/or SUBFRAME#Z and SUBFRAME#(G-P_X*R) (here, for example, “0 ≤ R ≤(the greatest (integer) H value satisfying a condition that “(G-P_X*H)”value is greater than or equal to the minimum subframe index valuewithin the (predefined (or assumed)) “(TXRESOURCE) SELECTION WINDOW”)are overlapped with each other). When the proposed rule (of (Example)#2)is applied, the number of resources reserved (or selected) by the V2X TXUE(s) (for example, (Exmaple#1)) may differ from the number of resourceswhose future behavior has to be monitored to determine collision (oroverlap) (for example, (Example#2)). At this time, as another example(of a case in which the corresponding rule is applied), when it is found(from (SUBFRAME#(N-10)) PSCCH decoding) that the V2X TX UE#Y hasreserved (or selected) a transmission resource on the SUBFRAME#(N-10)and SUBFRAME#(N+990) with a resource reservation (interval) period of“1000 ms”, and the V2X TX UE#X (having a resource reservation (interval)period of “100 ms”) performs (re)reservation(or selection) of atransmission resource at the SUBFRAME#N (the current time), thecandidate resource on the SUBFRAME#(N+90) (at the same (frequency)position of the V2X TX UE#Y) may be (finally) selected according towhether the candidate resource collides (or is overlapped) with thereserved (or selected) transmission resource (for example,SUBFRAME#(N+990)) of the V2X TX UE#Y when a (finite) number (for example“9”) (for example, the corresponding (finite) number may be set by the(greatest) (integer) value while the maximum value of the monitoringsubframe index does not exceed the time point for the reserved (orselected) transmission resource (for example, SUBFRAME#(N+990)) of theV2X TX UE#Y) of transmissions (for example, SUBFRAME#(N+90),SUBFRAME#(N+190), SUBFRAME#(N+290), SUBFRAME#(N+390), SUBFRAME#(N+490),SUBFRAME#(N+590), SUBFRAME#(N+690), SUBFRAME#(N+790), SUBFRAME#(N+890))assumed (or considered) by the candidate resource is performed. Since nocollision (or overlap) occurs in the corresponding example, thecandidate resource may be (finally) selected. In one example, NUM_EXTXvalue and FINI_SFNUM value (see (Example#1)) may be set (or signaled)independently (or differently) (or in the same manner). The FINI_SFNUMvalue may be set (or signaled) by a common value (or independent value)among the V2X UE (GROUP) ((sharing a V2X resource pool) on the samecarrier (or frequency)) (and/or NUM_EXTX value may be set (or signaled)by an independent value (which is set by the upper layer of the UE, forexample) among the V2X UE (GROUP) ((sharing a V2X resource pool) on thesame carrier (or frequency)) (or a common value)).

(Example#3) When a (selected) counter value is decreased by a predefined(or signaled) value (for example, “1”) every (actual) TB (or packet)transmission, if a TB (or packet) to be transmitted to the V2X TX UE#Mdoes not exist (for a long time) (in a (LOW LAYER) buffer (and/or PDCPLAYER)) (and/or if no (actual) TB (or packet) transmission isperformed), decrease of the (selected) counter value will be stopped,and when a TB (or packet) to be transmitted is again generated (after along time period) (and/or when (actual) TB (or packet) transmission isperformed), the (corresponding) V2X TX UE#M regards (or assumes) that(previously) reserved (or selected) resources are still available (sincethe (selected) counter value is a positive integer value) and therebydoes not use the (corresponding) resources properly.

The UE is able to reselect a reserved transmission resource, and the(corresponding) transmission resource (re)reservation (or selection)operation may be (at least) triggered when the (transmission resource(re)reservation) counter value (SEL_CNTVAL) selected randomly within arange (for example, “5-15”) predefined (or signaled) by the V2X TX UE(s)becomes “0” (and/or a “negative integer value”). Here, when the UEactually performs transmission, the counter value may be decreased by‘1’, and when the counter value becomes 0, the UE may perform a resourcere-reservation operation. In other words, in this case, the transmissionresource re-reservation may be made (triggered) only when the UEactually performs transmission (on a (previously) reserved resource).

As described above, the counter value (which triggers resourcere-reservation) is decreased only when the UE actually performs packettransmission (on a (previously) reserved resource). While a (finite)number of (previously) reserved resources are all passed (on the timeregion), if the corresponding counter value does not become “0” (and/ora “negative integer value”), a deadlock problem (a situation in whichresource re-reservation is never triggered) may occur.

Therefore, to solve the aforementioned problem, in what follows, amethod for performing resource re-reservation (namely resourcereselection) (even when the counter value does not become 0) will bedescribed with reference to related drawings

FIG. 24 is a flow diagram of a method for a UE to reselect a resourceaccording to one embodiment of the present invention.

Referring to FIG. 24 , the UE determines whether a resource reselectioncondition is satisfied S2410 The resource reselection may depend on aplurality of conditions. If at least one condition is satisfied amongthe plurality of resource reselection conditions, the UE may performresource reselection. In one example, (to solve the correspondingproblem), if there is not a TB (or packet) to be transmitted for morethan a predefined (or signaled) threshold (time) value (in the (LOWLAYER) butter (and/or PDCP LAYER)) (and/or if (actual) TB (or packet)transmission is not performed (continuously)) (and/or if the (current)subframe index exceeds 10240 (or TNUM_V2XSF) and/or if the (finitenumber of) subframes (or resources) reserved (or selected) by the V2X TXUE#M are (all) passed (in the time region)), the V2X TX UE#M (whose(selected) counter value is a positive integer value) may be made toperform a transmission resource (re)reservation (or selection)operation, but the (transmission resource (re)reservation) counter valuemay be made to be selected (randomly) (or (instead of newly (randomly)selecting the counter value), the (transmission resource(re)reservation) counter value may use (or maintain or apply) anexisting value (SEL_CNTVAL) (or the remaining value (or a predefined (orsignaled) (other) value)).

To summarize, resource reselection conditions for a UE may include (A) acase in which there is no more resources left for V2X transmission (forexample, as described above, a case where ‘the subframes (or resources)reserved (or selected) by the UE are (all) passed’), (B) a case in whichthe UE does not perform packet transmission for 1 continuous second (forexample, as described above, a case where ‘(continuous) TB (or packet)transmission is not performed for more than a predefined (or signaled)threshold time value’), and (C) a case in which the UE skips apredetermined number of consecutive transmission opportunities (forexample, as described above, a case where ‘TB (or packet) transmissionis not performed (continuously) for more than a predefined (or signaled)threshold value’). In what follows, a specific example of theaforementioned resource reselection condition will be described.

(A) The case where no more resources are left for v2X transmission

When no more resources related to a configured sidelink grant are left,the UE may perform resource reselection. In other words, if no moreresources related to a configured sidelink grant are left but there is anew MAC PDU to be transmitted to the UE, resource reselection may betriggered (in other words, in the aforementioned case, the UE mayperform resource reselection).

In one example, while the (corresponding) finite number of (and/orTNUM_V2XSF) reserved (or selected) subframes (or resources) are (all)passed (in the time region) (and/or a predefined (or signaled) subframeindex (for example, 10240 (or TNUM_V2XSF)) passes), if the (selected)counter value does not become “0” (and/or a “negative integer value”),the V2X TX UE(s) may be made to perform a transmission resource(re)reservation (or selection) operation, but the (transmission resource(re)reservation) counter value may be made to be selected (randomly) (or(instead of newly (randomly) selecting the counter value), the(transmission resource (re)reservation) counter value may use (ormaintain or apply) an existing value (SEL__CNTVAL) (or the remainingvalue (or a predefined (or signaled) (other) value)).

(B) The case where the UE does not perform packet transmission for onecontinuous second

If transmission or retransmission is not performed (by an MAC entity) ona resource indicated by a configured sidelink grant for (last) 1 second,the UE may perform resource reselection. In other words, when the UEdoes not perform transmission or retransmission for a continuoustransmission opportunity lasting 1 second, resource reselection may betriggered.

(C) The case where the UE skips a predetermined number of consecutivetransmission opportunities

If the UE is configured with a predetermined value and the number ofunused transmission opportunities (on a resource indicated by aconfigured sidelink grant) is the same as the predetermined value, theUE may perform resource reselection. In other words, if a specific valueis set for the UE and the UE skips as many transmission opportunities asthe specific number continuously, the UE may perform resourcereselection.

In other words, if the UE skips N (which is a positive integer)consecutive transmission opportunities, resource reselection may betriggered. Here, when the aforementioned condition is applied, the N isset for the UE, where N may take a value from [1, 2, 3, 4, 5, 6, 7, 8,9].

For example, if the UE skips ‘5’ consecutive transmission opportunitiesand is configured to perform resource reselection, the UE may performresource reselection when not performing transmission for 5 consecutivetransmission opportunities.

Afterwards, if the resource reselection condition is satisfied, the UEmay perform reselection of a resource with which V2X communication isperformed S2420. In other words, if the resource reselection conditionis satisfied, the UE may reselect a resource with which V2Xcommunication is performed, after which the UE may perform V2Xcommunication on the selected resource. For example, as described above,when (A) a case in which there is no more resources left for V2Xtransmission (for example, as described above, a case where ‘thesubframes (or resources) reserved (or selected) by the UE are (all)passed’), (B) a case in which the UE does not perform packettransmission for 1 continuous second (for example, as described above, acase where ‘(continuous) TB (or packet) transmission is not performedfor more than a predefined (or signaled) threshold time value’), \or (C)a case in which the UE skips a predetermined number of consecutivetransmission opportunities (for example, as described above, a casewhere ‘TB (or packet) transmission is not performed (continuously) formore than a predefined (or signaled) threshold value’), the UE mayreselect a resource with which V2X communication is performed andperform V2X communication on the selected resource.

Afterwards, the UE may perform V2X communication by using the selectedresource S2430. Here, as described above, the selected resource mayindicate the resource determined on the basis of a selection windowconstructed within a range satisfying the LATENCY REQUIREMENT (in otherwords, a resource on the selection window satisfying the latencyrequirement). Also, as described above (or below), the UE may select asubframe within the selection window on the basis of a sensing resultobtained by performing sensing in a UE-specific sensing period,determine transmission reservation resources on the basis of theselected subframe, and perform V2X communication on the reservedresource. Since a specific example in which the UE performs V2Xcommunication on the basis of a selected resource is the same asdescribed above (or below), specific details will be omitted.

Here, in one example, the term of the (corresponding) “transmissionresource (re)reservation (or selection) operation” may be interpreted as(A) re-reserving (or selecting) a transmission resource (different from(or the same as) the existing resource) on the basis of a sensing resultwhen the V2X TX UE(s) determines not to maintain (or reuse) a(transmission) resource selected previously on the basis of a(predefined (or signaled)) probability value (KEEP_P) (or irrespectiveof the corresponding probability value (KEEP_P)) and/or (B) the V2X TXUE(s)’s maintaining (or reusing) a (transmission) resource selectedpreviously on the basis of a (predefined (or signaled)) probabilityvalue (KEEP_P) (or irrespective of the corresponding probability value(KEEP_P)) and/or (C) reserving (or selecting) (again) a finite number(or a predefined (or signaled) (other) number (which, for example, isinterpreted to be larger than (or larger than or equal to) SEL_CNTVALvalue (and/or a value derived from the SEL_CNTVAL value)) of subframeswhich are the same as existing subframes (or the same resources (as theexisting ones)).

(Example#4) In one example, (when the V2X TX UE#U performs(re)reservation (or selection) of a transmission resource and/ordetermines the position of a selected (or reserved) subframe (orresource) of other V2X TX UE#Z) if a finite (or infinite) number of(reserved (or selected)) subframes (or resources) having a resourcereservation (interval) period of “P” exceed the (previous) 10240-thsubframe (for example, the “Z”-th subframe (here, in one example, “Z” isa positive integer value larger than “10240”)), the V2X TX UE#U may bemade to consider (or assume) that reservation (or selection) (of asubframe (or resource)) is performed with the resource reservation(interval) period “P” (again) from the “MOD (Z, 10240)”-th subframewithin the next (or following) 10240 subframes.

(Example#5) (in the case of (Example#1) and/or (Example#2) and/or(Example#3) and/or (Example#4)) reservation (or selection) (of a finite(or infinite) number of subframes (or resources)) itself may beperformed (by the V2X UE(s)) while the reservation (or selection) isallowed to exceed the SFN range (or TNUM_V2XSF range) (by applying SFNWRAP AROUND), and the V2X UE(s) may be made to perform to skip strange(time point) subframes (or resources) (from valid transmission subframes(or resources)) (and/or to extend the SFN range (or TNUM_V2XSF range)for reservation (or selection) of (a finite (or infinite) number of)subframes (or resources)) while maintaining the resource reservation(interval) period “P” of the V2X UE(s).

(Example#7) In one example, the following describe a method forsupporting an efficient (V2X message (or TB)) transmission operation ofthe V2X TX UE(s). In what follows, it is assumed that the UE reserves10*C subframes at the intervals of the resource reservation period P,where C may represent SL_RESOURCE_RESELECTION_COUNTER determined by theMAC.

(A) As described above, the UE’s reserving 10*C subframes at theintervals of the resource reservation period P may raise largely twoproblems.

First, although the UE reserves a finite number of subframes,SL_RESOURCE_RESELECTION_COUNTER may be decreased only when the MAC PDUis transmitted. Therefore, when the upper layer stops packet generationfor a specific time period and transmission is skipped in a large numberof reserved subframes, reserved resources for the UE may become nolonger valid, and no more resources may be available for transmission ofa newly arrived packet.

Also, if the time period of a set of reserved subframes exceeds a D2DFRAME NUMBER (DFN) range (namely, 10*C*P > T_(max), where T_(max) is10240 or 10176), a subframe number in the second DFN range may not bedivided by 100 (namely, division by 100 may give a remainder).

For example, as shown in FIG. 22 , if a V2X subframe has an index rangeof 10240, and the UE reserves subframes having an index of (0, 100, ...,10200, 10300, ..., 14900}, the subframe number from 10300 to 14900exceeds the DFN range; therefore, only the subframes having an index of{0, 100, ..., 10200, 60, 160, ..., 3660} may be reserved.

(B) In this regard, a method for solving the aforementioned two problemswill be provided in what follows.

First of all, to solve the first problem, whenSL_RESOURCE_(_)RESELECTION_COUNTER is still larger than 0 even if nomore resources reserved by the UE are left, the UE may extend resourcereservation.

To solve the second problem, the number of reserved subframes may beconfigured independently from the counter value. Moreover, the number ofreserved subframes may be configured to be smaller than the countervalue. For example, when resource reservation is triggered, the UE mayreserve a set of subframes up to the boundary of the DFN range.

FIG. 25 illustrates one example of a method for performing resourcereservation by taking into account the proposal described above.

According to FIG. 25 , by considering the aforementioned two proposalstogether, the UE may first determine a set of subframes terminatedbefore the DFN boundary and repeat resource reservation at the sameresource reservation intervals if more resources are required.

(C) The aforementioned proposal may be summarized as follows.

Proposal 1: when SL__RESOURCE RESELECTION COUNTER is still larger than 0even when the UE does not have reserved resources any more, the UE mayextend resource reservation.

Proposal 2: when resource reservation is triggered, the UE may reserve aset of subframes up to the boundary of a current DFN range.

One example of a transmission resource (re)reservation (or selection)operation of the V2X TX UE(s) may be described as shown in Table 2.

TABLE 2 2. Description of one example of the transmission resource(re)reservation (or selection) operation of the V2X TX UE(s) 2.1. UEprocedure for determining subframes and resource blocks for transmittingPhysical Sidelink Shared CHannel (PSSCH) and reserving resources forsidelink transmission mode 4) The number of subframes in one set of timeand frequency resources for transmission opportunities of the PSSCH isgiven as C _(resel).At this time, if C _(resel) is configured, C_(resel) may be given as [10*SL_RESOURCE_RESELECTION_COUNTER], otherwise(namely C _(resel) is not configured), C_(resel) may be set to 1. Iftime and frequency resource related to PSSCH transmission correspondingto a sidelink grant for which a set of sub-channels at the subframe thesame set of sub-channels at subframes may be determined with respect toPSSCH transmissions corresponding to the same sidelink grant. Here, j::: 1, 2, ..., and the resource reservation interval between C _(resel)-1 and P_(rsvp) may be determined by upper layers. 2.2. UE procedure fortransmitting the PSCCH With respect to the sidelink transmission mode 4,the UE may configure the content of the SCI format 1 as follows. IfSL_RESOURCE_RESELECTION_COUTNER is larger than 1, the UE configures aresource reservation field as a resource reservation period determinedby upper layers separated from each other by P_(step). Here P_(step) maybe 100. Otherwise, the UE sets the resource reservation field to 0. 2.3.UE procedure for determining the subset of resources to be excluded inPSSCH resource selection in sidelink transmission mode 4 If requested byupper layers at the subframe n, the UE determines a set of resources tobe excluded from PSSCH transmission according to the following steps.The upper layer may determine the parameter corresponding to the numberof sub-channels used for PSSCH transmission in a subframe L_(subCH),parameter corresponding to a resource reservation interval determined bythe upper layer P_(rsvp_TX), and parameter corresponding to a prioritytransmitted by the UE according to the associated SCI format 1prio_(TX.) STEP 1) The candidate single subframe resource R_(x,y)withrespect to PSSCH transmission may be determined as a set of sub-channelsL_(subCH)adjacent to the subframe t_(y)^(SL) together with a sub-channelx+j, where j=0,...L_(subCH) -1. STEP 2) The UE monitors subframesn-1001, n-1000, n-999, ..., n-2 except for a subframe at which the UEperforms transmission. Based on the decoded PSCCH of monitored subframesand measured S-RSSI, the UE may perform the operation corresponding tothe following steps. STEP 3) Parameter Th_(a,b)may be set to the valuestarted by the i-th SL-ThresPSSCH-RSRP field in theSL-ThresPSSCH-RSRP-List-r14. At this time, i = a*8 + b+1. STEP 4) A setS_(A) may be initialized to a combination of all of candidate singlesubframe resources. A set S_(B)may be initialized to an empty set. STEP5) If the following condition is satisfied, the UE excludes a candidatesingle subframe resource R_(x,y) from the set S_(A). The UE may receivethe SCI format 1 from the subframe t_(m)^(SL). And the ‘resourcereservation’ field and the ‘priority’ field may specify P_(rsvp_RX)andprio_(RX) from the received SCI format 1, respectively. The measurementof PSSCH-RSRP according to the received SCI format 1 may be larger thanTh_(propTX) _(, prioRX) The same SCI format 1 supposed to have beenreceived from the subframe t_(m + P_(step) ⋅ P_(rsvp_RX))^(SL) may bedetermined according to resource blocks and a set of subframesoverlapped with R_(x,y+Prsvp_TX)*jwhere j = 0, 1, ..., C_(resel) -1 STEP6) If the number of candidate single subframe resources remaining in theset S_(A) is smaller than 0.2•M_(total), the STEP 4 may be repeated byusing the Th_(a,b)which has been increased by 3 dB. STEP 7) With respectto the candidate single subframe resource R_(x,y)remaining in the setS_(A), the metric E_(x,y) may be defined as a linear average of S-RSSImeasured in the sub-channel x+k, where k=0,...L_(subCH) - 1 with respectto the subframes monitored in the STEP 2. STEP 8) The UE may move thecandidate single subframe resource R_(x,y)from the set S_(A)to the setS_(B)together with the least metric E_(x,y). The present step may berepeated. STEP 9) A set S_(C) may be defined together with a set of allof candidate single subframe resources not belonging to the set S_(B).

(Example#6) In one example, the V2X TX UE(s) may be made to performtransmission resource (re)reservation (or selection) operation accordingto Table 2 (for example, the aforementioned (or following) “STEP 2 or3”). Here, the “RESOURCE RESERVATION FIELD (RR_FIELD)” value in the SCIformat may be set by the quotient (or value) (I_VALUE) obtained bydividing the “RESOURCE RESERVATION INTERVAL (RR_INV)” value (set (orsignaled) by the upper layer (of the UE)) by a predefined (or signaled)value (P_STEP) (for example, “P_STEP = 100”). Here, I_VALUE may be set(or signaled) to have a range of (maximum) “1 ≤ I_VALUE ≤ 10”. Here,selection of (or allowing) a specific I_VALUE may be determined in theform of “CARRIER (or POOL)-SPECIFIC NETWORK (PRE)CONFIGURATION” (throughpredefined signaling (for example, the X-th bit of a 10-bit bitmapindicates whether the X-th I_VALUE is selectable (or allowed)). Here,restriction of selection of a specific I_VALUE (I_RESVAL) may beinterpreted that (A) the RR_INV value of “I_RESVAL*P_STEP” value is notset (or signaled) (by the upper layer (of the UE)) and/or (B) that adifferent I_VALUE (rather than I_RESVAL) capable of expressing the mostapproximate value to the RR_INV (actually) desired (by the upper layer(of the UE)) has to be set (or signaled).

Meanwhile, when the UE performs transmission while sensing is conducted(in a sensing window), namely, a UE may not be able to perform sensing(due to the half-duplex problem) for a subframe within the sensingwindow in which V2X transmission is performed. At this time, when the UEperforms V2X message transmission on a subframe corresponding to thesubframe unable to perform sensing at specific periods, the UE is led totransmit a V2X message on the basis of the subframe which failed toperform sensing.

In this regard, in what follows, to solve the problem of a UE’stransmitting a V2X message on the basis of a subframe which has failedto perform sensing, a method for excluding a subframe (from a selectionwindow) related to the subframe in which the UE has failed to performsensing will be described with reference to related drawings.

FIG. 26 is a flow diagram of a method for excluding a subframe (from aselection window) related to the subframe in which the UE has failed toperform sensing according to one embodiment of the present invention.

Referring to FIG. 26 , the UE selects a subframe (from a selectionwindow), excluding a subframe (in the selection window) related to asubframe in which transmission has been performed during a sensingperiod S2610. In other words, excluding a subframe in the selectionwindow related to a subframe in which transmission has been performedduring the sensing period among a plurality of subframes in theselection window, the UE may select a subframe from the plurality ofsubframes except for the excluded subframe in the selection window.

Here, the subframe in the selection window related to a subframe inwhich transmission has been performed during a sensing period may beoverlapped with a subframe corresponding to the subframe in which the UEis unable to perform sensing according to a resource reservation periodof a selected subframe selected by the UE selects within the selectionwindow. For the convenience of understanding, the present descriptionswill be further elaborated with reference to a related drawing.

FIG. 27 illustrates an example in which a subframe (from a selectionwindow) related to a subframe in which the UE has failed to performsensing.

Referring to FIG. 27 , for example, a first subframe may be the subframein which the UE has failed to perform sensing. A subframe correspondingto the first subframe at a specific period may be assumed to be a thirdsubframe.

Here, when a second subframe is selected from the selection window, aplurality of subframes may be reserved according to a resourcereservation period for the selected second subframe, and if one (ormore) subframe among the reserved subframes overlaps the third subframe,the UE may not select the second subframe within the selection window(namely, the second subframe may be excluded from selection).

Referring again to FIG. 26 , to generalized the aforementionedoperation, for example, if the UE has failed to perform sensing (as aV2X message transmission is performed) in the subframe #k (within thesensing window) and the subframe #(y+P*j) and the subframe #(K+100*i)are overlapped with each other, the UE may exclude the subframe #ywithin the selection window from resource reservation selection. Here,as described above, the subframe #k corresponds to the subframe in whichthe UE has failed to perform sensing, and the subframe #y may indicate asubframe within the selection window. Also, the P may represent theresource reservation period of the UE, where, for example, P may have avalue of 100 ms. The j may assume a value of 0, 1, 2, ..., C__(resel)-1.As described above, C__(resel) may represent a value proportional to aspecific counter value (for example 10*SL_RESOURCE_RESELECTION_COUNTER).Since descriptions about a specific counter (namelySL_RESOURCE_RESELECTION_COUNTER) are the same as described above,specific descriptions thereof will be omitted. Also, i may represent anelement in a set which is restricted by a carrier-specific setting. Inother words, the i may represent a value allowed for reservation by theeNB and represent a value related to a specific period (for example, ifi is 2, the specific period (for example, 1 hop) is 100*i = 200 ms). Atthis time, i may have a value of 2, 4, 6, 8, for example.

In one example, in the STEP 5 of Table 2, if

SUBFRAME#(T_(M)^(SL))

has not been monitored from the V2X message transmission operation ofthe V2X TX UE(s) in the STEP 2 (and/or if PSCCH decoding related toother V2X TX UE(s) and (associated) PSSCH DM-RS RSRP (and/or S-RSSI)measurement operation has not been performed on the

SUBFRAME#(T_(M)^(SL))

due to the V2X message transmission operation) and R_(X,Y+RR_INVTX*j)among R_(X,Y) belonging to SA overlaps

SUBFRAME#(T_(M + I_CANVAL * P_STEP)^(SL))

(and/or (partial) resource(s) that may be selected (or reserved) byother V2X TX UE(s) on the

SUBFRAME#((T_(M + I_CANVAL * P_STEP)^(SL))),

the V2X TX UE(s) may be made to exclude R_(X,) _(Y) (additionally) fromthe set S_(A). Here, in one example, “J” may be defined to be “0, 1,..., or (C_(RESEL)-1) (refer to Table 2)”. Here, “RR_INVTX” mayrepresent “RESOURCE RESERVATION INTERVAL” (set (or signaled) from theupper layer) of the V2X TX UE(s), and “I_CANVAL” may be regarded(specifically) as the value(s) belonging to the selectable (orallowable) “I_VALUE SET” designated (previously) in the form of“CARRIER(/POOL)-SPECIFIC NETWORK (PRE)CONFIGURATION”. Here, if theaforementioned rule is applied, and whether to (additionally) excludeR_(X,) _(Y) from the set S_(A) is determined (as a resource (forexample,

SUBFRAME#((T_(M)^(SL)))

is not monitored from the V2X message transmission operation of the V2XTX UE(s) in the STEP 2), only the “I_VALUE SET” (and/or “RESOURCERESERVATION INTERVAL”) (actually) selectable (or allowable) (from aspecific carrier (or pool)) may be taken into account.

Afterwards, the UE may perform V2X communication on the basis of theselected subframe S2620 As described above, the selected subframe (orresource) may indicate a resource determined on the basis of theselection window constructed within a range satisfying the LATENCYREQUIREMENT (namely a resource on the selection window satisfying theLATENCY REQUIREMENT). Also, as described above (below), the UE mayselect a subframe within the selection window on the basis of a sensingresult obtained by performing sensing during a UE-specific sensingperiod, determine transmission reservation resources on the basis of theselected subframe, and perform V2X communication on the reservedresource. As described above, the UE’s performing V2X communication onthe subframe may indicate that V2X communication is performed on thesubframe reserved in conjunction with the subframe selected by the UE. Aspecific example in which the UE performs V2X communication on the basisof a selected resource is the same as described above (or below),detailed descriptions thereof will be omitted

As another example, in the STEP 5 of Table 2, if

SUBFRAME#(T_(M)^(SL))

has not been monitored from the V2X message transmission operation ofthe V2X TX UE(s) in the STEP 2 (and/or if PSCCH decoding related toother V2X TX UE(s) and (associated) PSSCH DM-RS RSRP (and/or S-RSSI)measurement operation has not been performed on the

SUBFRAME#(T_(M)^(SL))

due to the V2X message transmission operation) and R_(X,Y+RR)__(INVTX*j)among R_(X,Y) belonging to SA overlaps

SUBFRAME#(T_(M + I_CANVAL * P_STEP)^(SL))

(and/or (partial) resource(s) that may be selected (or reserved) byother V2X TX UE(s) on the

SUBFRAME#((T_(M + I_CANVAL * P_STEP)^(SL))),

, the V2X TX UE(s) may be made to exclude R_(X,Y) (additionally) fromthe set S_(A). Here, “I_CANVAL_X” may be set (or signaled) to themaximum value (or minimum value or a specific value) among the value(s)belonging to the selectable (or allowable) “I_VALUE SET” designated(previously) in the form of “CARRIER(/POOL)-SPECIFIC NETWORK(PRE)CONFIGURATION”. Here, as another example, in the STEP 5 of Table 2,if

SUBFRAME#(T_(Y − I_CANVAL * P_STEP)^(SL))

has not been monitored from the V2X message transmission operation ofthe V2X TX UE(s) in the STEP 2 (and/or if PSCCH decoding related toother V2X TX UE(s) and (associated) PSSCH DM-RS RSRP (and/or S-RSSI)measurement operation has not been performed on the

SUBFRAME#(T_(Y − I_CANVAL * P_STEP)^(SL))

due to the V2X message transmission operation), the V2X TX UE(s) may bemade to exclude RX, Y (additionally) from the set SA. Here, in oneexample, “(N - 1001) ≤ (Y - I_CANVAL*P_STEP) ≤ (N - 2)” (where, in oneexample, the SUBFRAME#N time point may be interpreted as the time atwhich a (transmission) resource (re)reservation (or selection) is set(or signaled) to be performed (by the upper layer)) (and/or “P_STEP =100”). In another example, in the STEP 5 of Table 2, if

SUBFRAME#(T_(Y − I_CANVAL_Q * P_STEP * K)^(SL))

has not been monitored from the V2X message transmission operation ofthe V2X TX UE(s) in the STEP 2 (and/or if PSCCH decoding related toother V2X TX UE(s) and (associated) PSSCH DM-RS RSRP (and/or S-RSSI)measurement operation has not been performed on the

SUBFRAME#(T_(Y − I_CANVAL_Q * P_STEP * K)^(SL))

due to the V2X message transmission operation), the V2X TX UE(s) may bemade to exclude R_(X,) _(Y) (additionally) from the set S_(A). Here, inone example, “(N - 1001) ≤ (Y - I_CANVAL_Q*P_STEP*K) ≤ (N - 2)” (where,in one example, the SUBFRAME#N time point may be interpreted as the timeat which a (transmission) resource (re)reservation (or selection) is set(or signaled) to be performed (by the upper layer)) (and/or “P_STEP =100”) and/or it may be defined so that “K = NON-NEGATIVE INTEGER”. Here,“I_CANVAL_Q” may be set (or signaled) to a value(s) belonging to theselectable (or allowable) “I_VALUE SET” (designated (previously) in theform of “CARRIER(/POOL)-SPECIFIC NETWORK (PRE)CONFIGURATION”) (and/orthe minimum value (or maximum value or a specific value) among thevalue(s) belonging to the selectable (or allowable) “I_VALUE SET”).Here, if the aforementioned (partial) rule is applied and whether to(additionally) exclude R_(X,) _(Y) from the set S_(A) is determined, (A)J value is assumed to have (only) a previously set (or signaled)specific value(s) (for example, “J = 1 (or 0)”) (and/or the J value (ora value(s) smaller than (or larger than) or equal to the corresponding,derived J value) at which “RR_INVTX*J” (or “P_STEP*J”) becomes the sameas the (actually) selectable (or allowable) maximum (or minimum)“RESOURCE RESERVATION INTERVAL” (or previously set (or signaled)specific “RESOURCE RESERVATION INTERVAL”) (on a specific carrier (orpool)) and/or (B) RR_INVTX value is assumed to have (only) a previouslyset (or signaled) specific value(s) (for example, “RR_INVTX = 1000 ms”)(and/or an (actually) selectable (or allowable) maximum (or minimum)“RESOURCE RESERVATION INTERVAL” (on a specific carrier (or pool)) (or avalue(s) smaller than (or larger than) or equal to the correspondingmaximum (or minimum) “RESOURCE RESERVATION INTERVAL”)). Here, theproposed method may be applied limitedly only when the priority relatedto a message (or packet) to be transmitted by the V2X TX UE(s) (and/or aCONGESTION LEVEL value related to the (corresponding) carrier (or pool))is smaller (or larger) than a predefined (or signaled) threshold value.

(Example#8) In one example, a method for effectively reflecting aresource (or subframe) not monitored (or sensed) due to the transmissionoperation (of the V2X UE(s)) in the “RESOURCE EXCLUSION PROCEDURE”(BASED ON PSSCH-RSRP MEASUREMENT)” will be described below.

When single transmission of a TB is performed by other UEs at thesubframe #k, it may be difficult to obtain accurate information ofPSSCH-RSRP on the skipped subframe #k. Therefore, if the subframe#(y+P*j) overlaps the subframe #(k+100*i), the UE#A may consider toexclude the subframe #k existing within the selection window of the UE.At this time, as described above, P may represent the resourcereservation interval of the UE, and j may assume 0, 1, ...,10*SL_RESOURCE_RESELECTlON_COUNTER-1. Also, i may indicate a (possible)element in a set restricted by a carrier-specific network (pre)setting.

Here, in one example, (when a V2X UE(s) having a “SHORTER RESOURCERESERVATION PERIOD (or INTERVAL)” on a predefined (or signaled)(specific) resource pool (and/or a V2X UE(s) performing transmission ofa V2X message (or traffic) having a (relatively) short period)(SHORTP_UE(s)), and a V2X UE(s) having a “(RELATIVELY) LONGER RESOURCERESERVATION PERIOD (or INTERVAL)” (and/or a V2X UE(s) performingtransmission of a V2X message (or traffic) having a (relatively) longperiod) (LONGP_UE(s)) exist together, the value of “100” in the“SUBFRAME#(K+100*I)” may be set to a (predefined (or signaled))different value (A) if a SHORTP_UE(s) performs a sensing operationand/or (B) if a LONGP_UE(s) performs a sensing operation (with respectto the SHORTP_UE(s)).

Along with the aforementioned method, the UE #A may exclude all of theresources (within the selection window of the UE) overlapped withtransmission of other UE that may be scheduled from a skipped subframe#k. In what follows, the operation above will be described withreference to related drawings.

FIGS. 28 to 30 illustrate an example reflecting a resource in the“RESOURCE EXCLUSION PROCEDURE (BASED ON PSSCH-RSRP MEASUREMENT.

Referring to FIGS. 28 to 30 , i may be restricted to a set such as {2,4}, and P and SL_RESOURCE_RESELECTION_COUNTER may be set to 200 ms and5, respectively.

In the case of FIG. 28 , due to “subframe#(k+100*2) (namely, i = 2) andsubframe#(y+200*0) (namely, j = 0)”, and “subframe#(k+100*4) (namely, i= 4) and subframe#(y+200*1) (namely, j = 1)”, the subframe #k (withinthe selection window) may be excluded from selection.

In the case of FIG. 29 , due to “subframe#(k+100*4) (namely, i = 4) andsubframe#(y+200*0) (namely, j = 0)”, the subframe#k may be excluded fromselection (within the selection window).

However, in the case of FIG. 30 , since there exists no subframe belongsto the selection window in which the aforementioned overlap occurs, nosubframe within the selection window may be excluded from selection.

As a result, the following method is provided.

Proposal: To process the subframe#k skipped (due to transmission by theV2X UE(s)) in the resource exclusion procedure, the following solutionmay be proposed. if the subframe#(y+P*j) may be overlapped with thesubframe#(k+100*i), the UE#a may have to exclude the subframe#y withinthe selection window of the UE#a. Here, P may represent the resourcereservation interval of the UE, j = 0, 1, ...,(10*SL_RESOURCE_RESELECTION_COUNTER-1), and i may represent all of the(possible) elements of a set limited by network (pre)setting for eachcarrier.

As another example, if a bitmap having a predefined (or signaled)(specific) length (for example, “16”, “20”, “100”) is applied repeatedlyfor V2X resource pool configuration, (in particular, as subframes set(or signaled) to be used for SLSS transmission are excluded from(candidate) subframes which may be set (or signaled) as a V2X resourcepool) a problem may be caused, where (application of) the correspondingbitmap is “TRUNCATED” at the “DFN RANGE END”. Here, to solve thecorresponding problem, the (existing) “DFN RANGE” value (for example,“10240” or “10176”) may be increased (which, for example, may beinterpreted in a so-called HYPER-SFN (or HYPER-DFN) form). Here, the(increased) “(maximum) DFN RANGE” value may be defined in the form of“10240 (or 10176)*H_VAL” (or “10240 (or 10176)*H_MAXVAL”) (and/or “MAXDFN RANGE*H_VAL” (or “MAX DFN RANGE*H_MAXVAL”)). Here, in one example,(A) a (currently applied) H_VAL value (or index), (B) H_VAL (index)range that may be configured (or used) and/or (C) the maximum value (ormaximum index) of H_VAL (H_MAXVAL) (and/or minimum value (or minimumindex) (H_MINVAL)) may be predefined (or signaled) by the network (or aserving cell) through predefined (upper (or physical) layer) signaling(and/or through a (newly defined) field on the PSBCH by the (SYNCH.SOURCE) UE (or through predefined D2D channel or signal)) (in the“CARRIER (or POOL or CELL)-SPECIFIC (PRE)CONFIGURATION”) form and/or asone of “V2X POOL (PRE)CONFIGURATION”).

FIG. 31 illustrates one example of a case in which the (existing) “DFNRANGE” value (for example, “10240” or “10176”) is increased. Here, it isassumed that H_VAL (and/or H_MAXVAL) value is set to “5” (which, forexample, is denoted as “H”). Here, the H_VAL value (and/or H_MAXVAL)(and/or V2X resource pool configuration (or signaling) related bitmapvalue) may be set (or signaled) (in a restrictive manner) so that the(increased) “(maximum) DFN RANGE” value may be divided by the V2Xresource pool configuration-related (set (or signaled)) bitmap length(without a remainder) (and/or so that (on the (whole) subframes set (orsignaled) as a V2X resource pool) ((on a specific carrier (or pool)) aperiod corresponding to the multiple of (actually) selectable (orallowable)) (maximum (or minimum) or predefined (or signaled)) “RESOURCERESERVATION INTERVAL” (for example, “100 ms”) may be “WRAPPED AROUND”(properly)). If the aforementioned rule is applied, the V2X UE(s)increases the H_VAL value by a predefined (or signaled) value (forexample, “1”) each time “the (maximum) DFN RANGE” value (for example,“1024 (or 10240)”) is reached and uses (or considers) a (V2X) subframein the ascending order of index starting from a relatively small valuewithin a (V2X) subframe (set) based on the same H_VAL value for (V2Xmessage) transmission (and/or V2X communication). As another example, inthe sensing operation, the “SUBFRAME INDEX” uses the “LOGICAL INDEX”within the (V2X) resource pool. Here, in one example, when the “TDM”scheme is applied to a (predefined) other signal and a (V2X) resourcepool, a physical time interval may become relatively large. In thiscase, the V2X TX UE(s) may make a smaller value be used for the“RESOURCE RESERVATION INTERVAL”.

Meanwhile, when the aforementioned rule is applied (for example, asdescribed above, when the (existing) “DFN RANGE” value (for example,“10240” or “10176”) is increased (which, for example, may be interpretedas a kind of HYPER-SFN (or HYPER-DFN) method)), V2X communication may beperformed as follows.

(A) (For example, when a bitmap for a V2V subframe is not repeated aninteger number of times during a DFN period of [RANI, RAN2]), V2V may beperformed by being multiplexed with other signal or channel.

(B) Currently, the DFN range for V2V, namely Tmax which represents thenumber of subframes that may be allocated for V2V may be 10240 or 10176depending on SLSS resource configuration.

Meanwhile, the length of a bitmap representing a V2V subframe for aresource pool may be 16, 20, or 100. Therefore, as described above (forexample, in the case of FIG. 22 ), there may be a case in which the DFNrange is not divided exactly by the bitmap length unit.

A fundamental solution to solve the problem may be to change the DFNrange (namely, Tmax) so that the DFN range may be always divided exactlyby the bitmap length. This may involve extending the DFN range so thatit may be a multiple of the bitmap length. Therefore, to extend the SFNrange, a concept of “Hyper SFN (H-SFN)” may be introduced.

Here, if H-SFN is provided by SystemInformationBlockTypel-BR, theboundary between the BL UE within CE and a modification period for a UEmay be defined by the SFN value, which is expressed as (H-SFN*1024+SFN)mod m = 0. Here, H-SFN may always be provided with respect to NB-IoT,and the modification period boundary may be defined by the SFN valuewhich is expressed as (H-SFN*1024+SFN) mod m = 0. The modificationperiod may be configured by system information.

In order to enable notification of system information update to theRRC_IDLE UE which has an eDRX period longer than or equal to themodification period, an eDRX acquisition period may be defined. Theboundary of the eDRX acquisition period may be determined by the H-SFNvalue which is expressed as H-SFN mod 256 = 0. In particular, in thecase of NB-IoT, the boundary of an eDRX acquisition period may bedetermined by the H-SFN value which is expressed as H-SFN mod 1024 = 0.

FIG. 32 illustrates one example of transmitting updated systeminformation.

Referring to FIG. 32 , if the network changes (part of) systeminformation, the network may first notify UEs of this change. At thenext modification period, the network may transmit updated systeminformation. If update notification is received, the UE may obtain newsystem information immediately from the start of the next modificationperiod by using a DRX cycle shorter than or equal to the modificationperiod.

The system information transmitted, namely SystemInformationBlockType1may be defined as shown in Table 3 below.

TABLE 3 SystemInformationBlockType1-v1310-IEs ::= SEQUENCE {      hyperSFN-r13   BIT STRING (SIZE (10))   OPTIONAL. -- Need OR      eDRX-Allowed-r13      ENUMERATED {true}      OPTIONAL, -- Need OR

Here, ‘hyperSFN’ represents a hyper SFN which is increased by one eachtime the SFN is wrapped around, and existence of the ‘eDRX-Allowed’field represents whether DRX with an extended idle mode is allowed in acell. If eDRX is not allowed, the UE has to stop using the DRX in theextended idle mode.

By applying a similar principle, the DFN range may be extended bydefining a “hyper DFN”. (In other words, except for the SLSS sub-frame),the V2V subframe index in the logical domain may be given by (H-DFN *T_(max) + DFN).

H_(max), which is the maximum value of the H-DFN, may be configured sothat it may be divided exactly by the length of a bitmap amounting toH_(max) * T_(max) which is a total number of potential V2V subframes.

FIG. 33 illustrates one example of a hyper DFN.

In the present example, H_(max) may be set to 5. (In other words,H-DFN#5 is reset to H-DFN#0.) To support the hyper DFN, the currentH-DFN index needs to be synchronized not only among UEs sharing the sameresource pool but also between an eNB and a UE. The H-DFN index may besignaled as part of elements constituting a resource pool between theeNB and the UE and signaled through the PSBCH. When GNSS is asynchronization reference, the H-DFN index may be derived from thecurrent UTC value.

(C) To conclude,

The hyper DFN may be proposed as follows to process discontinuity in therepetition of a subframe bitmap.

Proposal 1: The hyper DFN may be defined to increase the DFN range asmuch as the amount of H_(max). The V2V subframe index of the logicaldomain may be provided by (H -DFN*T_(max) + DFN) according to which theH-DFN is increased after T_(max) subframe, where H-DFN = 0, 1, ...,H_(max) - 1.

Proposal 2: H_(max) may be set to the value obtained by dividingH_(max)*T_(max) by the length of the V2V subframe bitmap of a resourcepool.

Proposal 3: The current H-DFN may be signaled as part of elementsconstituting a resource pool from the eNB. And the current H-DFN mayalso be signaled through the PSBCH.

As another example, in the aforementioned example, H_(max) value(without additional signaling) may be fixed (on the specification) as apredefined value. Here, the H_(max) value may be fixed to “25” (or “amultiple of 25”). Table 4, 5, and 6 show analysis data related to thedescriptions above.

TABLE 4 1 SLSS SF 10176 Bit-map length candidates Bit-map lengthcandidates 16 20 100 16 20 100 H_max 1 0 16 76 H_max 51 0 16 76 2 0 1252 52 0 12 52 3 0 8 28 53 0 8 28 4 0 4 4 54 0 4 4 5 0 0 80 55 0 0 80 6 016 56 56 0 16 56 7 0 12 32 57 0 12 32 8 0 8 8 58 0 8 8 9 0 4 84 59 0 484 10 0 0 60 60 0 0 60 11 0 16 36 61 0 16 36 12 0 12 12 62 0 12 12 13 08 88 63 0 8 88 14 0 4 64 64 0 4 64 15 0 0 40 65 0 0 40 16 0 16 16 66 016 16 17 0 12 92 67 0 12 92 18 0 8 68 68 0 8 68 19 0 4 44 69 0 4 44 20 00 20 70 0 0 20 21 0 16 96 71 0 16 96 22 0 12 72 72 0 12 72 23 0 8 48 730 8 48 24 0 4 24 74 0 4 24 25 0 0 0 75 0 0 0 26 0 16 76 76 0 16 76 27 012 52 77 0 12 52 28 0 8 28 78 0 8 28 29 0 4 4 79 0 4 4 30 0 0 80 80 0 080 31 0 16 56 81 0 16 56 32 0 12 32 82 0 12 32 33 0 8 8 83 0 8 8 34 0 484 84 0 4 84 35 0 0 60 85 0 0 60 36 0 16 36 86 0 16 36 37 0 12 12 87 012 12 38 0 8 88 88 0 8 88 39 0 4 64 89 0 4 64 40 0 0 40 90 0 0 40 41 016 16 91 0 16 16 42 0 12 92 92 0 12 92 43 0 8 68 93 0 8 68 44 0 4 44 940 4 44 45 0 0 20 95 0 0 20 46 0 16 96 96 0 16 96 47 0 12 72 97 0 12 7248 0 8 48 98 0 8 48 49 0 4 24 99 0 4 24 50 0 0 0 100 0 0 0

TABLE 5 2 SLSS SF 10112 Bit-map length candidates Bit-map lengthcandidates 16 20 100 16 20 100 H_max 1 0 12 12 H_max 51 0 12 12 2 0 4 2452 0 4 24 3 0 16 36 53 0 16 36 4 0 8 48 54 0 8 48 5 0 0 60 55 0 0 60 6 012 72 56 0 12 72 7 0 4 84 57 0 4 84 8 0 16 96 58 0 16 96 9 0 8 8 59 0 88 10 0 0 20 60 0 0 20 11 0 12 32 61 0 12 32 12 0 4 44 62 0 4 44 13 0 1656 63 0 16 56 14 0 8 68 64 0 8 68 15 0 0 80 65 0 0 80 16 0 12 92 66 0 1292 17 0 4 4 67 0 4 4 18 0 16 16 68 0 16 16 19 0 8 28 69 0 8 28 20 0 0 4070 0 0 40 21 0 12 52 71 0 12 52 22 0 4 64 72 0 4 64 23 0 16 76 73 0 1676 24 0 8 88 74 0 8 88 25 0 0 0 75 0 0 0 26 0 12 12 76 0 12 12 27 0 4 2477 0 4 24 28 0 16 36 78 0 16 36 29 0 8 48 79 0 8 48 30 0 0 60 80 0 0 6031 0 12 72 81 0 12 72 32 0 4 84 82 0 4 84 33 0 16 96 83 0 16 96 34 0 8 884 0 8 8 35 0 0 20 85 0 0 20 36 0 12 32 86 0 12 32 37 0 4 44 87 0 4 4438 0 16 56 88 0 16 56 39 0 8 68 89 0 8 68 40 0 0 80 90 0 0 80 41 0 12 9291 0 12 92 42 0 4 4 92 0 4 4 43 0 16 16 93 0 16 16 44 0 8 28 94 0 8 2845 0 0 40 95 0 0 40 46 0 12 52 96 0 12 52 47 0 4 64 97 0 4 64 48 0 16 7698 0 16 76 49 0 8 88 99 0 8 88 50 0 0 0 100 0 0 0

TABLE 6 NO SLSS SF 10240 Bit-map length candidates Bit-map lengthcandidates 16. 20 100 H_max 1 0 0 40 H_max 51 0 0 40 2 0 0 80 52 0 0 803 0 0 20 53 0 0 20 4 0 0 60 54 0 0 60 5 0 0 0 55 0 0 0 6 0 0 40 56 0 040 7 0 0 80 57 0 0 80 8 0 0 20 58 0 0 20 9 0 0 60 59 0 0 60 10 0 0 0 600 0 0 11 0 0 40 61 0 0 40 12 0 0 80 62 0 0 80 13 0 0 20 63 0 0 20 14 0 060 64 0 0 60 15 0 0 0 65 0 0 0 16 0 0 40 66 0 0 40 17 0 0 80 67 0 0 8018 0 0 20 68 0 0 20 19 0 0 60 69 0 0 60 20 0 0 0 70 0 0 0 21 0 0 40 71 00 40 22 0 0 80 72 0 0 80 23 0 0 20 73 0 0 20 24 0 0 60 74 0 0 60 25 0 00 75 0 0 0 26 0 0 40 76 0 0 40 27 0 0 80 77 0 0 80 28 0 0 20 78 0 0 2029 0 0 60 79 0 0 60 30 0 0 0 80 0 0 0 31 0 0 40 81 0 0 40 32 0 0 80 82 00 80 33 0 0 20 83 0 0 20 34 0 0 60 84 0 0 60 35 0 0 0 85 0 0 0 36 0 0 4086 0 0 40 37 0 0 80 87 0 0 80 38 0 0 20 88 0 0 20 39 0 0 60 89 0 0 60 400 0 0 90 0 0 0 41 0 0 40 91 0 0 40 42 0 0 80 92 0 0 80 43 0 0 20 93 0 020 44 0 0 60 94 0 0 60 45 0 0 0 95 0 0 0 46 0 0 40 96 0 0 40 47 0 0 8097 0 0 80 48 0 0 20 98 0 0 20 49 0 0 60 99 0 0 60 50 0 0 0 100 0 0 0

As another example, (A) when a bitmap having a predefined (or signaled)(specific) length is applied repeatedly to designate a V2X resource pooland/or (B) when a (periodic) transmission resource(s) on the “RESOURCERESERVATION INTERVAL” (set (or signaled) from the upper layer (of theUE)) is reserved (or selected), (part of) V2X resource designated by the(corresponding) bitmap and/or (part of) (periodic) transmission resourcereserved (or selected) (by the V2X TX UE(s)) may be positioned on a WANcommunication-related DL (time (or frequency)) resource (for example,“DL SF and/or “(TDD) SPECIAL SF” (and/or “DWPTS”)).

Meanwhile, when the UE performs V2X message transmission on a specificcarrier, the UE may not perform V2X message transmission by using all ofthe subframes on the carrier. In this regard, by taking into account asubframe in which the UE does not perform V2X message transmission, anexample of a method for transmitting a V2X message will be describedwith reference to related drawings.

FIG. 34 is a flow diagram of a method for performing V2X communicationon an allocated V2X resource pool according to one embodiment of thepresent invention.

Referring to FIG. 34 , the UE may allocate a V2X resource pool to theremaining subframes except for a specific subframe S3410. At this time,the specific subframe may represent (A) SLSS subframe, (B) DL and S(Special) subframe in the case of a TDD shared carrier, or (C) reservedsubframes. In what follows, a more specific example in which a subframeexcluded from V2X transmission will be described.

(A) About the SLSS subframe

First, the UE may allocate a V2X resource pool for the remainingsubframes except for the SLSS subframe.

More specifically, the SLSS subframe may be excluded from the mappingaccording to a (repeated) V2V pool bitmap (namely a bitmap (orinformation) indicating the subframes to which a V2X pool may beallocated), and at this time, the bitmap length may be 16, 20, or 100.The bitmap may define which subframe allows V2V SA and/or datatransmission and/or data reception. An example in which an SLSS subframeis excluded from V2X transmission will be described as follows.

FIG. 35 illustrates an example in which an SLSS subframe is excludedfrom V2X transmission.

FIG. 35 assumes that the subframe number may have a value of 0, 1, ...,10239 (namely, a total of 10240 subframes), a V2X bitmap is repeated inunits of 10 subframes, and the V2X bitmap is [0110101101],

When a V2X logical index is allocated, the UE may allocate a V2X logicalindex with respect to the subframes except for the SLSS subframe. Forexample, if it is assumed that the subframe index #3, #163, and so oncorrespond to the SLSS subframe (where the SLSS subframe is repeated inunits of 160 subframes), the V2X UE may allocate a V2X logical index tothe remaining subframes (namely the remaining subframes except for theSLSS subframe) except for the subframe index #3, #163, and so on(S3510). Here, it may be assumed that a V2X resource is allocatedaccording to the V2X bitmap with respect to the subframe allocated bythe V2X logical index.

At this time, the V2X logical index derived through the aforementionedprocess may not correspond to an integer multiple of the V2X bitmap. Forexample, when the SLSS subframe is allocated in units of 160 subframes,64 SLSS subframes may be defined among 10240 subframes as describedabove, and accordingly, the V2X logical index may be allocated to 10176subframes corresponding to 10240 - 10264.

As described above, when it is assumed that the V2X logical index may beallocated to the 10176 subframes, and the V2X bitmap period is 10, thelogical index is not divided exactly by the V2X bitmap period. In otherwords, when a V2X bitmap having a period of 10 is allocated to 10176subframes, there may be chances that bits are not allocated to 6subframes.

Therefore, the UE may exclude as many subframes as the number ofnon-allocated subframes may be excluded from allocation of V2X logicalindex S3520. At this time, subframes not allocated may be evenlydistributed.

(B) About DL and SPECIAL (S) subframe

In the case of a TDD (shared) carrier, DL and/or SPECIAL (S) subframemay be excluded from the mapping due to a (repeated) V2V full bitmap. Anexample in which DL and/or SPECIAL (S) subframe is excluded from V2Xtransmission will be described below with reference to related drawings.

FIG. 36 illustrates an example in which DL and S subframe are excludedfrom V2X transmission.

FIG. 36 assumes that the subframe number may have a value of 0, 1, ...,10239 (namely a total of 10240 subframes), the V2X bitmap is repeated inunits of 10 subframes, and the V2X bitmap is [0110101101].

When the V2X logical index is allocated, the UE may allocate the V2Xlogical index to the subframe except for DL and/or SPECIAL (S) subframe(and/or SLSS subframe). For example, if it is assumed that the subframeindex #7 (and so on) corresponds to the DL and SPECIAL (S) subframe, theV2X UE may allocated the V2X logical index to the remaining subframesexcept for the subframe index #7 (and so on) S3610. Here, the UE mayallocate a V2X resource according to the V2X bitmap with respect to asubframe allocated by the V2X logical index.

Afterwards, the UE may exclude as many subframes as a number ofnon-allocated subframes additionally to the allocation of V2X logicalindex S3520. At this time, non-allocated subframes may be evenlydistributed.

(C) The case of a reserved subframe

A resource pool is composed of a plurality of reserved subframes so thatthe bitmap is repeated an integer number of times within a specificrange (for example, D2D Frame Number (DFN) range). For example, the V2X(for example, V2V) logical subframe index may not be allocated to areserved subframe. Moreover, the position of a reserved subframe may bemarked implicitly.

To summarize, the corresponding problem occurs because the bitmaprelated to the V2X resource pool configuration is appliedunconditionally to WAN communication-related DL/UL (time (or frequency))resources except only for (predefined (or signaled)) V2X SYNC. SIGNALtransmission-related (time (or frequency)) resources (for example, V2XSYNCH. SUBFRAME(s)) (and/or because of the DFN WRAP AROUND problem (orphenomenon). Here, to solve the corresponding problem, the V2X TX UE(s)may be made to (A) assume that (part of) V2X resources (designated bythe bitmap) on the WAN communication related DL (time (or frequency))resources are not valid (in terms of (V2X pool-related) “LOGICALINDEXING”) and/or (B) to skip (V2X message (or TB)) transmissionoperation for (part of) (periodic) transmission resources reserved (orselected) (by the V2X TX UE(s)) on the WAN communication-related DL(time (or frequency)) resources (and/or instead of skipping the (V2Xmessage (or TB)) transmission operation, the (V2X message (or TB))transmission operation may be (re)performed on the (closest) valid (oravailable) V2X resource after the transmission operation. Here, in theformer case, (V2X pool-related) “LOGICAL INDEXING” may be regarded asbeing performed by involving (or excluding) the invalid resource (forexample, DL (time (or frequency)) resource) (for example, whentransmission timing of a specific period is determined on the “LOGICALINDEX”, a problem in which an actual transmission period becomes(excessively) larger than an intended (target) period may bealleviated). In another example, when a bitmap having a (specific)predefined (or signaled) length is applied repeatedly, the WANcommunication-related DL (time (or frequency)) resource (for example,“DL SF” and/or “(TDD) SPECIAL SF” (and/or “DWPTS”)) may be(additionally) excluded (for example, it may be regarded that the (V2Xpool-related) “LOGICAL INDEXING” is not performed (or applied) to thecorresponding resource excluded (additionally)), and the bitmap may bemade to be applied (by taking into account only the WANcommunication-related UL (time (or frequency)) resource). Here, the rulemay be applied limitedly only to the “IN-COVERAGE” environment (and/orTDD system).

Referring again to FIG. 34 , the UE may perform V2X communication on anallocated V2X resource pool S2420. A specific example in which the UEperforms V2X communication is the same as described above.

In one example, the rule may be extended to be applied to the case where(part of) V2X resources (designated by a bitmap) and/or (part of)(periodic) transmission resources reserved (or selected) (by the V2X TXUE(s)) are positioned not only on the WAN communication-related DL (time(or frequency)) resources but also on the resources with which(predefined (or signaled)) V2X communication is not performed properly(for example, (time (or frequency) resource) in addition to “UL SF”(and/or “UPPTS”) (and/or a resource having a relatively higher priority(than the priority related to a V2X message to be transmitted) for whicha (specific) V2X channel (or signaling) transmission (or reception) isset).

In another example, the V2X UE(s) (within coverage of an eNB) may bemade to transmit an “offset value for the DFN#0 based on GNSS” signaled(or defined) previously (by a (serving) eNB) to other V2X UE(s) (outsidethe coverage of the eNB) through a predefined channel (for example,PSBCH).

In a yet another example, if I_VALUE (range) value and/or “RESOURCERESERVATION INTERVAL” (range) value selectable (or allowable) on a V2Xresource pool (and/or (V2X) carrier) is limited (in the form of“CARRIER(/POOL)-SPECIFIC NETWORK (PRE)CONFIGURATION”), the V2X TX UE(s)may be made, on the corresponding V2X resource pool (and/or (V2X)carrier), to perform a sensing operation (for example, STEP 5 of Table2) (and/or energy measurement operation (for example, STEP 8 of Table2)) on the basis of (A) a period value that may be derived (orcalculated) from the minimum value (I_MINVAL) of I_VALUE (or maximumvalue) (or a (specific) I_VALUE predefined (or signaled)) (for example,“I_MINVAL*P_STEP) and/or (B) the minimum (or maximum) period value of“RESOURCE RESERVATION INTERVAL” (or predefined (or signaled)) (specific)“RESOURCE RESERVATION INTERVAL” value). Here, when a specific V2Xresource pool is set (or allowed) only for a P-UE(s) performing V2Xmessage transmission with a relatively long period (for example, “500ms”) (compared with the V-UE(s)) and the aforementioned rule is applied,the P-UE(s) performs a sensing operation (and/or energy measurementoperation) based on the (corresponding) period (for example, “500 ms”).

Meanwhile, as described above, the UE may select a random value from aninterval between 5 and 15 in the case of a relatively long resourcereservation period (for example, a resource reservation period longerthan 100 ms) (which is called “L_PER”) and reserve as many resources asthe selected value multiplied by 10. However, applying the resourcereservation method described above to the case of using a relativelyshort resource reservation period (for example, 20 ms or 50 ms (shorterthan 100 ms)) (which is called “S_PER”) may be inappropriate for anL_PER UE existing in the same resource pool to sense an S_PER UE.

In this regard, if a (relatively) “SHORTER RESOURCE RESERVATION PERIOD(or INTERVAL)” (for example, “20 ms”) is employed in order for a UE tosupport transmission of a V2X message (or traffic) having a (relatively)short period, (part of) the following parameters may be set (orsignaled) differently (or independently) (when compared withtransmission of a V2X message (or traffic) performed with a (relatively)long period (or a predefined (or signaled) (threshold) period) (forexample, “100 ms”). In one example, it may be interpreted that (part of)the following parameters are applied to (A) the case where SHORTP_UE(s)performs a sensing operation and/or (B) the case where LONGPUE(s)performs a sensing operation (with respect to the SHORTP_UE(s)) (when aV2X UE(s) having a “SHORTER RESOURCE RESERVATION PERIOD (or INTERVAL)”(and/or a V2X UE(s) performing transmission of a V2X message (ortraffic) having a (relatively) short period) (SHORTP_UE(s)) and a V2XUE(s) having a “(RELATIVELY) LONGER RESOURCE RESERVATION PERIOD (orINTERVAL)” (and/or a V2X UE(s) performing transmission of a V2X message(or traffic) having a (relatively) long period) (LONGP_UE(s)) co-existon a predefined (or signaled) (specific) resource pool). In whatfollows, the present method will be described with reference to relateddrawings.

FIG. 37 is a flow diagram of a method for performing reservation of aV2X transmission resource when resource reservation is set with arelatively short period (for example, 20 ms or 50 ms (shorter than 100ms)) according to one embodiment of the present invention.

Referring to FIG. 37 , when resource reservation is set with arelatively short period, the UE may perform reservation of a relativelylarge number of V2X transmission resources S3710. Here, reserving arelatively large number of V2X transmission resources does not indicateselecting a random number from an interval between 5 and 15 andreserving as many resources as the selected value multiplied by 10 asdescribed above, but indicates that the UE selects a random value froman interval between 5*K (where K is a positive integer larger than orequal to 2) and 15*K and reserves as many resources as the selectedvalue multiplied by 10.

In other words, in the case of a relatively short resource reservationperiod (for example, 20 ms, 50 ms), the aforementioned counter value (avalue of 5 or more and 15 or less) is multiplied by 5 or 2, which isfurther multiplied by 10. Then as many resources as the finalmultiplication result may be reserved.

For example, if the resource reservation period is ‘20 ms’, the UE mayselect a random value from the interval of [5*5, 15*5] (in other words,5*2 or more and 15*5 or less), and as many resources as the randomnumber multiplied additionally by 10 may be reserved. According to thepresent example, the UE may reserve more than 250 and less than 750resources.

In another example, if the resource reservation period is ‘50 ms’, theUE may select a random value from the interval of [5*2, 15*2], and asmany resources as the random number multiplied additionally by 10 may bereserved. According to the present example, the UE may reserve more than100 and less than 300 resources.

(Example#1) A finite number of subframes (having a resource reservation(interval) period) assumed (or used) when transmission resource (re)reservation (or selection) is performed (and/or C_(resel) value of Table2 (for example, “[10 * SL_RESOURCE_RESELECTION_COUNTER]”)). Here, in thecase of transmission of a V2X message (or traffic) having a (relatively)short period, the corresponding finite number of subframes (having theresource reservation (interval) period) (and/or the C_(resel) value) maybe set (or signaled) to have a relatively small number (which, forexample, provides an effect of preventing excessive reservation (orselection) of resources from being performed (within a short timeperiod)

Afterwards, the UE may perform V2X communication on the reserved V2Xtransmission resource S3720. A specific example in which the UE performsV2X communication on the reserved V2X transmission resource is the sameas described above.

FIG. 38 is a flow diagram of a method for performing sensing with arelatively short period when resource reservation with a short period isset according to one embodiment of the present invention.

Referring to FIG. 38 , if resource reservation with a short period isset, the UE performs sensing in a sensing period with a relatively shortperiod to determine a resource with which V2X communication is performedS3810. In other words, as described above, if resource reservation witha short period is set (for example, when resource reservation is setwith a period shorter than 100 ms), the sensing (namely S-RSSImeasurement) period may be set as a resource reservation period used fortransmission by the UE. In other words, if resource reservation is setwith a short period, the UE may perform sensing according to the shortperiod used for resource reservation. In what follows, the operationabove will be described in more detail.

(Example#2) The V2X message priority (which, for example, may be set (orsignaled) with a relatively low (or high) priority) and/or the“PSSCH-RSRP MEASUREMENT” threshold value in the STEP 5 of Table 2(and/or “0.2*M_(total)″-related coefficient (or ratio) in the STEP 6 (or8) of Table 2 (which, for example, may be interpreted as a ratio forderiving (or determining) the minimum number of (candidate) resourcesthat have to be remained (in the SA set) (among all of the (candidate)resources) after the STEP 5 of Table 2 is performed and/or a ratio forderiving (or determining) the (minimum) number of (candidate) resourcesthat have to be remained in the SB set after the STEP 8 of Table 2 isperformed)) may be set (or signaled) to have a different (orindependent) value and/or the “PSSCH-RSRP MEASUREMENT” increase (forexample, “3 DB”) applied when the minimum number of (candidate)resources that have to be remained within the SA set (among all of the(candidate) resources) after the STEP 5 of Table 2 is performed is notsatisfied and/or the period value (and/or a period value used for energymeasurement operation (for example, STEP 8 of Table 2) used for thesensing operation (for example, the STEP 5 of Table 2) (for example, inthe STEP 8 of Table 2, the value of “100 ms” may be changed (to arelatively short (or long) value)) may be set (or signaled) to have adifferent (or independent) value.

(Example#3) I_VALUE (range) selectable (or allowable) on a V2X resourcepool (and/or (V2X) carrier) and/or P_STEP value

(Example#4) (OPEN-LOOP) parameter (or value) related to transmissionpower (for example, “PO”, “ALPHA”) and/or V2X resource pool (or carrier)

As another example, the V2X UE(s) may be made to perform (transmission)resource (re)selection as follows.

The V2X UE may select a transmission resource by using the followingmethod.

It is assumed that the UE operates in a mode in which the UE itselfperforms resource selection. In the aforementioned mode, if resourceselection/reselection for V2X message transmission is triggered, the UEmay perform sensing and select or reselect a resource on the basis ofthe sensing result. The UE may transmit scheduling assignment (SA) whichindicates the selected or reselected resource.

For example, at the subframe (which may also be called TTI in thefollowing) #n, resource selection or reselection may be triggered forthe UE Then, the UE may perform sensing between the subframe#n-1 and thesubframe#n-b (where a > b > 0, a and b are integer numbers) and selector reselect resources for V2X message transmission on the basis of thesensing result.

The a and b may be the values set commonly to V2X UEs or the values setindependently for individual V2X UEs.

When the a and b are common to V2X UEs, for example, a relationship suchas ‘a = 1000 + b’ may hold. In other words, if the UE is triggered toselect a resource for V2X message transmission by itself, the UE mayperform a sensing operation for 1 second (1000 ms = 1000 subframes =1000 TTIs).

The UE may consider all of SA transmissions decoded over the periodstarting from the subframe#n-a to the subframe#n-b. The decoded SA maybe associated with data transmission over the period starting from thesubframe#n-a to the subframe#n-b, where the decoded SA may consider thedata transmitted before the subframe#n-a.

A UE which has failed to perform a sensing operation at the subframe#mmay exclude subframes#(m+100*k) from resource selection or reselection(because of such a reason that a signal has to be transmitted from thesubframe#m). Meanwhile, the UE may skip the subframes used fortransmitting a signal without performing a sensing operation.

After performing the sensing, the UE may select a time or frequencyresource for PSSCH, namely a sidelink data channel.

The UE may transmit scheduling assignment (SA) from the subframe#n+c.The c is an integer larger than 0, which may be a fixed value or avariable. The UE may not be requested to transmit scheduling assignment(namely PSCCH transmission) for the subframes the c values of which aresmaller than cmin. The cmin may be a fixed value or set by the network.

The scheduling assignment (SA) transmitted from the subframe#n+c mayindicate associated data transmitted from the subframe#n+d. d may be aninteger larger than or equal to c (d≥c). Both of c and d may be a valuesmaller than or equal to 100.

Meanwhile, if either of the following conditions is met, reselection ofa V2X resource may be triggered.

(A) The case where the counter satisfies a termination condition

The counter decreases its value at each transmission of a transmissionblock and may be reset if reselection is triggered for all ofsemi-statically selected resource. The reset value may be randomlyselected between 5 and 15, for example, with an equal probability.

(B) The case where transmission blocks are not suitable for the currentresource allocation even if an allowed maximum Modulation and CodingScheme (MCS) is used

(C) The case where reselection is indicated by the upper layer

Meanwhile, if all of PSCCH or PSSCH transmissions have the samepriority, selection or reselection of a PSSCH resource may be performedthrough the following steps.

(A) STEP 1:

First, it is assumed that anyhow, all of the resources are selectable.

(B) STEP 2:

Specific resources are excluded on the basis of scheduling assignmentdecoding and additional conditions. At this time, the UE may select oneof the following two options.

The first option excludes the resources indicated or reserved by decodedscheduling assignment and the resources whose DM-RS power received fromdata resources associated with the scheduling assignment is larger thana threshold value.

The second option excludes the resources indicated or reserved bydecoded scheduling assignment and the resources whose energy measuredfrom data resources associated with the scheduling assignment is largerthan a threshold value.

(C) STEP 3:

The UE may select a V2X transmission resource among the resources whichhas not been excluded.

For example, after measuring and ranking the remaining PSSCH resourceson the basis of total received energy, the UE may select a subset. TheUE may compare the energy of currently selected resources with theenergy in the subset, and if the energy in the currently selectedresources is larger than a threshold value with respect to the energy inthe subset, select one from among the subset. The UE may randomly selectone resource from among the subset.

Similarly, after measuring and ranking the remaining PSSCH resources onthe basis of total received energy, the UE may select a subset. The UEmay randomly select one resource from among the subset.

Similarly, after measuring and ranking the remaining PSSCH resources onthe basis of total received energy, the UE may select a subset. The UEmay randomly select a resource which minimizes fragmentation offrequency resources from among the subset.

In one example, when the (transmission) resource (re)selection operationis performed according to Table 2, the following (partial) rules may beapplied additionally.

[Proposed Rule#10] In one example, according to the ‘LATENCY (or QoS)REQUIREMENT’ (and/or ‘PRIORITY’ and/or ‘SERVICE TYPE’) of a (generated)packet (to be transmitted), it may be interpreted as ‘(D or C - M)’((maximum (or minimum)) range) (which, for example, may be interpretedas ‘TX RESOURCE (RE)SELECTION DURATION (or RANGE or WINDOW)’) (forexample, ‘M’ is a ‘(LOW LAYER) buffer’ (and/or the time point at which a(generated) packet (or message) (to be transmitted) (on the ‘PDCPLAYER’) arrives (or is received) (or the time point at which a packet(or message) is generated); also, (here) ‘D (or C)’ wording may indicatethat a resource (re)selection (or reservation) operation is triggered(exceptionally) differently (which, for example, may be regarded as thetransmission time point of (initial) data (PSSCH) (or controlinformation (PSCCH)) after SUBFRAME#N). In another example, the ‘C’and/or ‘D’ ((maximum (or minimum)) range) (which, for example, may beinterpreted as ‘TX RESOURCE (RE)SELECTION DURATION (or RANGE orWINDOW)’) has to be determined to satisfy (or by taking into account)the ‘LATENCY (or QoS) REQUIREMENT’ which may differ according to the‘SERVICE TYPE’ (and/or ‘PRIORITY LEVEL’). Here, the ‘UPPER LIMIT (orLOWER BOUND)’ of ‘C’ and/or ‘D’ (which, for example, may be interpretedas ‘TX RESOURCE (RE)SELECTION DURATION (or RANGE or WINDOW)’) may not befixed. Here, the corresponding ‘UPPER LIMIT (or LOWER BOUND)’ may be set(or signaled) differently according to ‘PRIORITY LEVEL’ (and/or ‘SERVICETYPE’ and/or ‘LATENCY (or QoS) REQUIREMENT’). Here, if a currentlyselected ‘D’ value (or ‘SUBFRAME#D’) has a problem in satisfying the‘LATENCY (or QoS) REQUIREMENT’ of a newly arrived (or generated (orreceived)) packet (or message), a (transmission) resource (re)selectionoperation may be triggered. In one example, the maximum (and/or minimum)or range (which, for example, may be interpreted as ‘TX RESOURCE(RE)SELECTION DURATION (or RANGE or WINDOW)’) of the ‘D’ (and/or ‘C’ )value may be determined by taking into account the ‘(LOW LAYER) buffer’(and/or the time point at which a (generated) packet (or message) (to betransmitted) (on the ‘PDCP LAYER’) arrives (or is received) (or the timepoint at which a packet (or message) is generated) (‘M’) and/or the timepoint at which the (transmission) resource (re)selection operation istriggered (as a predefined (or signaled) condition is satisfied) (‘N’)and/or ‘LATENCY REQUIREMENT’ (‘L’) (for example, ‘100 ms’) and/or ‘PPPP’of a packet (or message) (for example, when a (partially) different‘PPPP’ value is set (or allowed) for each packet (or message) ofdifferent ‘LATENCY REQUIREMENT’). As one specific example, the maximum(and/or minimum) value of ‘D’ (and/or ‘C’) may be determined by‘(L-ABS(M-N))’ or ‘MIN(L, (L-ABS(M-N)))’ (where, for example, ‘MIN(X,Y)’ and ‘ABS(Z)’ represent a function returning the minimum valuebetween ‘X’ and ‘Y’ and a function returning the absolute value of ‘Z’,respectively) or the range of ‘D’ (and/or ‘C’) may be designated by‘(L - ABS(M-N)) < D(/C) < 100 (or ‘LATENCY REQUIREMENT’)’ (or ‘(L -ABS(M-N)) ≤ D(/C) ≤ 100 (or ‘LATENCY REQUIREMENT’)′). In one example,considering retransmission of a specific (one) ‘TB (or packet ormessage)’, when the maximum value (and/or minimum value) of ‘D’ (and/or‘C’) value is calculated (or determined), a predefined (or signaled)‘MARGIN (or OFFSET)’ value (‘MAG_VAL’) may have to be subtracted fromthe ‘L’ value. When the corresponding rule is applied, the maximum(and/or minimum value) of ‘D’ (and/or ‘C’) value may be determined as‘((L-MAG_VAL) - ABS(M-N))’ or ‘MIN((L - MAG_VAL), ((L - MAG_VAL) -ABS(M-N)))’. Here, the ‘MAG_VAL’ value may have ‘DEPENDENCY’ on thenumber of retransmissions (for example, the ‘MAG_VAL’ value is increasedas the number of retransmissions is increased). The rule may be appliedlimitedly only for a case where the ‘(transmission) resource(re)selection operation’ is triggered (according as a (predefined (orsignaled)) condition is satisfied), and a (generated) packet (ormessage) (to be transmitted) exists on the ‘(LOW LAYER) buffer’ (and/or‘PDCP LAYER’) (or when a packet (or message) is generated) In anotherexample, when a (generated) packet (or message) (to be transmitted) doesnot exist on the ‘(LOW LAYER) buffer’ (and/or ‘PDCP LAYER’) although the‘(transmission) resource (re)selection operation’ is triggered(according as a (predefined (or signaled)) condition is satisfied) (orwhen there is no generated packet (or message)), the (transmission)resource (re)selection operation may be performed by assuming (orconsidering) that ‘(N = M)’ (which, for example, may be interpreted thatthe time at which the (transmission) resource (re)selection option istriggered (‘N’) is assumed (or considered) to be the time (‘M’) at whicha (generated) packet (or message) (to be transmitted) is received on the‘(LOW LAYER) buffer’ (and/or ‘PDCP LAYER’)) or by deferring the(transmission) resource (re)selection operation until a (generated)packet (or message) (to be transmitted) arrives (or is received)actually on the ‘PDCP LAYER’ (or until a packet (or message) is actuallygenerated) or by assuming that a (generated) packet (or message) (to betransmitted) has arrived (or has been received) (or exists) on the ‘PDCPLAYER’ (previously including (or not including) the ‘N’ time point) (ora packet (or message) has been generated). As another example,subsequent resources including (or not including) the time pointcorresponding to the maximum value (for example, ‘(LABS(M-N))’, ‘100 (or‘LATENCY REQUIREMENT’)′) of the (aforementioned) ‘D’ (and/or ‘C’) areassumed (or considered) as unavailable and may be made to be excluded(from (re)selectable candidate resources) (on the ‘STEP 3 (or 2)’). Inan additional example, resources at the time point (for example,resources before the time point including (or not including) ‘(C +C_MIN)’ (or resources between ‘N’ time point and ‘(C+C_MIN)’ time point(here, in one example, the resources corresponding to the ‘N’ time pointand ‘(C+C_MIN)’ time point may be included (or may not be included))))corresponding to the minimum value (C_MIN) (for example, the ‘minimumvalue’ may be determined (for example, ‘4 ms’) by taking into accountthe ‘PROCESSING TIME’ of the UE) of ‘C’ (and/or ‘D’) (where, forexample, the time point ‘C’ may be interpreted as the time point atwhich transmission of the (first) control (or scheduling) information(PSCCH) is performed after the (transmission) resource (re)selectionoperation is triggered (‘N’)) is assumed (or considered) to beunavailable and may be made to be excluded from (re)selectable candidateresources (on ‘STEP 2 (or 3)’). In a still another example, according to(part of) the proposed rule of the present invention (for example,[Proposed Rule#1] and [Proposed Rule#10]), when the ‘TX RESOURCE(RE)SELECTION DURATION (or RANGE or WINDOW)’ ((maximum (or minimum)range) is set (or changed) differently by taking into account ‘PRIORITYLEVEL’ (and/or ‘SERVICE TYPE’ and/or ‘LATENCY (or QoS) REQUIREMENT’),the following (partial) parameters related to the sensing operation(and/or (transmission) resource (re)selection (or reservation) operation(and/or V2X message transmission)) according to whether a predefinedcondition is satisfied. Here, the (corresponding) condition may bedefined as (A) the case in which a V2X message with the ‘LATENCYREQUIREMENT’ shorter (or longer) than a predefined (or signaled)threshold is transmitted (and/or the case in which a V2X message withthe ‘PPPP’ higher (or lower) than a predefined (or signaled) thresholdis transmitted), and/or (B) the case in which a number of (selectable)(candidate) resources (for example, subframes) less (or more) than apredefined (or signaled) threshold exist (or remain) within the ‘TXRESOURCE (RE)SELECTION DURATION (or RANGE or WINDOW)’ (and/or the casein which the minimum (or maximum) value of the ‘TX RESOURCE(RE)SELECTION DURATION (or RANGE or WINDOW) is smaller (or larger) thana predefined (or signaled) threshold value.

(Example#10-1) In the case of a V2X message having ‘LATENCY REQUIREMENT’shorter (or longer) than the (V2X message-related) PPPP value (or range)(for example, a predefined (or signaled) threshold), the correspondingtransmission may be secured by selecting a relatively high (or low) PPPPvalue (or range). Here, in the case of transmission based on a high (orlow) PPPP value (or range), whether a resource employed by other UE forthe corresponding transmission is selectable (or IDLE or BUSY) isdetermined on the basis of a relatively low (or high) PSSCH-RSRPthreshold value (and/or in the case of a V2X message having the ‘LATENCYREQUIREMENT’ longer (or shorter) than predefined (or signaled)threshold, even if the ‘LATENCY REQUIREMENT’ has the same PPPP value (orrange), by setting (or signaling) a relatively low (or high) PSSCH-RSRPthreshold value, V2X message transmission having the ‘LATENCYREQUIREMENT’ shorter (or longer) than a predefined (or signaled)threshold value may be secured). And/or when the minimum ratio (ornumber) of candidate (transmission) resources that need to be remained(and/or the corresponding ratio (or number) of remaining candidate(transmission) resources) is smaller than a predefined (or signaled)threshold value after the candidate (transmission) resource exclusionoperation based on a sensing operation execution interval (or period)and/or a ((maximum (or minimum)) period (or range) from which acandidate (transmission) resource may be selected (SELECTION WINDOW)and/or a range from which a random value is determined (or selected) todefine a maintenance interval of a (re)selected (or reserved) resource(and/or a coefficient multiplied to the corresponding selected randomvalue (for deriving the C_(RESEL) value [1/2/3]) and/or resourcereservation period and/or PSSCH-RSRP threshold value, when the minimumratio (or number) of candidate (transmission) resources that needs to beremained after the candidate (transmission) resource exclusion operationbased on the offset value added to the (related) PSSCH-RSRP thresholdvalue and/or S-RSSI is smaller than a predefined (or signaled) thresholdvalue, when a V2X message having the ‘LATENCY REQUIREMENT’ shorter (orlonger than) a (predefined (or signaled) threshold value), for example,is transmitted, (and/or a V2X message having the ‘PPPP’ higher (orlower) than a predefined (or signaled threshold value is transmittedand/or when a number of (selectable) (candidate) resources less (ormore) than a predefined (or signaled) threshold exist (or remain) withinthe ‘TX RESOURCE (RE)SELECTION DURATION (or RANGE or WINDOW)’ and/orwhen the minimum (or maximum value) of the ‘TX RESOURCE (RE)SELECTIONDURATION (or RANGE or WINDOW)’ is smaller (or larger) than a predefined(or signaled) threshold, when (A) the minimum ratio (or the minimumnumber) of candidate (transmission) resources that have to be remainedafter a candidate (transmission) resource exclusion operation based onthe PSSCH-RSRP threshold value is performed and/or (B) the ratio (or thenumber) of the corresponding remaining candidate (transmission)resources is smaller than a predefined (or signaled) threshold value,the minimum ratio (or the minimum number) of candidate (transmission)resources that have to be remained after the candidate (transmission)resource exclusion operation based on the offset value added to the(related) PSSCH-RSRP threshold value and/or (C) S-RSSI is performed maybe set to a relatively high value (which, for example, brings an effectof relieving the increase of probability of collision). And/or CBRthreshold value used for determining whether a (sub)-channel is BUSY (orIDLE) and/or a RADIO-LAYER PARAMETER SET allowed (or restricted) (foreach PPPP/CBR) (for example, maximum transmission power, the number(range) of retransmissions per TB, MCS value (or range), maximum limit(CR_LIMIT) of OCCUPANCY RATIO, and so on) [1/2/3].

[Proposed Rule#11] In one example, the ‘(TIMER) EXPIRATION CONDITION’related to (transmission) resource (re)selection may be defined as acondition where (part of) the following conditions are satisfied(simultaneously). In one example, the present rule may be interpretedthat only when (part of) the following conditions are satisfiedsimultaneously, (actually) (it is considered (or assumed) that the(transmission) resource (re)selection operation has been triggered), theV2X UE(s) is made to perform the (transmission) resource (re)selectionoperation.

(Example#11-1) The case where the counter value (which decreases by apredefined value (for example, ‘1’) for each TB transmission) is changedto ‘0’ (and/or a ‘negative integer value’).

(Example#11-2) The case where there exists a (generated (or received))packet (or message) (to be transmitted) on the ‘(LOW LAYER) buffer’(and/or ‘PDCP LAYER’) (and/or the case where a packet (or message) isgenerated)

[Proposed Rule#12] In one example, while the counter value (whichdecreases by a predefined value (for example, ‘1’) for each TBtransmission) satisfies the ‘EXPIRATION CONDITION’ (for example, thecase where the counter value is changed to ‘0’ (and/or a ‘negativevalue’)) (and/or (according as a predefined (or signaled) condition issatisfied), the ‘(transmission) resource (re)selection operation’ istriggered), if there is no (generated (or received)) packet (or message)(to be transmitted) on the ‘(LOW LAYER) buffer’ (and/or ‘PDCP LAYER’)(or if a packet (or message) has not been generated), the V2X UE(s) maybe made to assume that (the most recent) packet (or message) reaches (orgenerates (or receives)) the ‘INTERVAL (or PERIODICITY)’ observedpreviously (or recently), and if it happens that a problem (for example,the case in which the (re)selected (transmission) resource does notsatisfy the ‘LATENCY (or QoS) REQUIREMENT’) actually occurs (afterwards)after the (transmission) resource (re)selection is performed, to performthe (transmission) resource (re)selection operation additionally.

In one example, according to the following method (along with the rulesdescribed in Table 2), a V2X UE(s) may be made to perform (transmission)resource (re)reservation.

d may be a value less than or equal to d_(max.) d_(max) may bedetermined depending on the priority such as UE, data, or service type.

The UE may inform of whether to reuse a frequency resource for a signaltransmitted from the subframe#n+d for potential transmission of othertransmission block at the subframe#n+e. Here e is an integer, and d<e.The UE may inform of whether to reuse the frequency resource explicitlyor implicitly. The e value may be one value or a plurality of values.Also, additionally, the UE may inform that subsequent to the subframe#n+e, the frequency resource for a signal transmitted from thesubframe#n+d will not be used.

A receiving UE receiving a V2X signal decodes scheduling assignment (SA)transmitted by a transmitting UE transmitting a V2X signal. At thistime, it may be assumed that the same frequency resource may be reservedat the subframe#n+d+P*j (j = i, 2*i, ..., J*i) due to the schedulingassignment. The P may be a value of 100. The J value may be explicitlysignaled by the scheduling assignment or a fixed value (for example, 1).The i value may be signaled explicitly by the scheduling assignment, ora predetermined value or a fixed value. Similarly, the i value may be aninteger between 0 and 10.

[Proposed Rule#13] In one example, since the V2X TX UE(s) is made tosignal the “I” value (refer to the aforementioned I) through SA (field),the V2X RX UE(s) becomes able to figure out at which time point the V2XTX UE(s) (additionally) reserves (or uses) the same frequency resourceindicated (or scheduled) through the (corresponding) SA (for example,when the V2X TX UE signals “I” value as “2”, the V2X RX UE(s) assumesthat the same frequency resource indicated (or scheduled) through the(corresponding) SA on the “TTI#(N+D)” and “TTI#(N+D+2*P)” has beenreserved). In what follows, for the convenience of description, it isassumed that the “I” value is selected (4 bits) from a predefined (orsignaled) range of “[0, 1, ..., 10]” and/or “J” value is fixed to “1”(refer to the aforementioned J). In one example, when it is difficultfor the V2X TX UE(s) to accurately predict (its) V2X MESSAGE generationperiod as the V2X MESSAGE generation period is changed according to thepredefined parameter (for example, velocity or amount of (movement)direction change), it may not be efficient to reserve a (future)resource according to the method. As one method to solve thecorresponding problem, when a specific V2X TX UE(s) signals the “I”value (on the SA field) as “2”, it is assumed that the same frequencyresource (HARD_RSC) indicated (or scheduled) through the (corresponding)SA on the “TTI#(N+D)” and “TTI#(N+D+2*P)” has been reserved in a“explicit (or hard)” manner, but the same frequency resource (SOFT_RSC)(indicated (or scheduled) through the (corresponding) SA) at the timepoint (for example, “TTI#(N+D+1*P)”, “TTI#(N+D+3*P)”, “TTI#(N+D+4*P)”,“TTI#(N+D+5*P)”, “TTI#(N+D+6*P)”, “TTI#(N+D+7*P)”, “TTI#(N+D+8*P)”,“TTI#(N+D+9*P)”, “TTI#(N+D+10*P)”) based on (not signaled through the SA(field)) the remaining “I” values has been reserved in a “POTENTIAL (orSOFT)” manner. Here, in one example, the corresponding rule (and/orSOFT_RSC reservation) may be applied only for a (predefined or signaled)specific RESOURCE ALLOCATION MODE (which, for example, may not beapplied for RESOURCE SELECTION based on the MODE 1 and/or RANDOMRESOURCE SELECTION (or PARTIAL SENSING) of P-UE). When the correspondingrule is applied, the V2X TX UE(s) may be made to apply a predefined (orsignaled) different (DM-RS POWER or ENERGY MEASUREMENT) threshold valuewhen the HARD_RSC and SOFT_RSC of other V2X TX UE(s) (determined on thebasis of SA decoding) are determined whether they are selectablecandidate resources or resources to be excluded according to the “DM-RSPOWER or ENERGY MEASUREMENT” value (STEP 2 of Table 2). In one example,a HARD_RSC-related threshold (HARD_TH) may be set (or signaled) to belower (or higher) than that (SOFT_TH) of a SOFT_RSC (which, for example,may be interpreted that the HARD_RSC is protected with a relativelyhigher priority than the SOFT_RSC). Here, the SOFT_RSC-related thresholdmay be set (or signaled) in the form of an offset value (HARD_THOFF)with respect to the HARD_RSC (and/or the HARD_TH-related threshold maybe set (or signaled) in the form of an offset value (SOFT_THOFF) withrespect to the SOFT_RSC). Here, in one example, (A) if the HARD_THOFF isset (or signaled) to “0”, other V2X TX UE(s) determines whether toexclude the HARD_RSC and SOFT_RSC (of the corresponding V2X TX UE(s))(STEP 2 of Table 2) at the same priority according to the “DM-RSPOWRE/ENERGY MEASUREMENT” value (or interprets that the (corresponding)V2X TX UE(s) attempts to reserve the same frequency resource (set orscheduled through the (corresponding) SA) on the time point based on allof the “I” values), (B) if the HARD_THOFF is set (or signaled) to the“infinity (or relatively large value)”, other V2X TX UE(s) always (orwith a very high probability) determines (STEP 2 of Table 2) theSOFT_RSC (of the corresponding V2X TX UE(s)) as a selectable candidateresource. Here, in one example, (A) V2X MESSAGE PRIORITY of other V2X TXUE(s) discovered from SA decoding (and/or V2X MESSAGE PRIORITY that theV2X TX UE(s) itself attempts to transmit) and/or (B) the (corresponding)threshold value (for example, HARD_TH and SOFT TH) for each (measured)“CONGENSTION LEVEL” (or offset value (for example, HARD_THOFF (orSOFT_THOFF)) set (or signaled) differently) and/or (C) V2X MESSAGEPRIORITY of other V2X TX UE(s) figured out from SA decoding (and/or V2XMESSAGE PRIORITY that the V2X TX UE(s) itself attempts to transmit)and/or (D) the (corresponding) threshold (for example, HARD_TH andSOFT_TH) (or offset value (for example, HARD THOFF (SOFT_THOFF))) may beadjusted according to the “CONGESTION LEVEL”. Here, by applying apredefined (or signaled) different offset value to the “DM-RSPOWER/ENERGY MEASUREMENT” value related to the HARD_RSC and SOFT_RSC ofother V2X TX UE(s) (determined from SA decoding), the V2X TX UE(s) maydetermine whether the HARD_RSC and SOFT_RSC are selectable candidateresources or resources to be excluded (STEP 2 of Table 2). Here, theHARD_RSC related offset value (for example, it is assumed as a “negativeinteger”) may be set (or signaled) larger (or smaller) than that of theSOFT_RSC (for example, it may be interpreted that the HARD_RSC isprotected with a relatively high priority compared with the SOFT_RSC).Here, only the offset value with respect to the SOFT_RSC (orHARD_RSC)-related “DM-RS POWER/ENERGY MEASUREMENT” value may be set (orsignaled). Here, in one example, (A) V2X MESSAGE PRIORITY of other V2XTX UE(s) discovered from SA decoding (and/or V2X MESSAGE PRIORITY thatthe V2X TX UE(s) itself attempts to transmit) and/or (B) the(corresponding) offset value set (or signaled) differently for each(measured) “CONGENSTION LEVEL” and/or (C) V2X MESSAGE PRIORITY of otherV2X TX UE(s) figured out from SA decoding (and/or V2X MESSAGE PRIORITYthat the V2X TX UE(s) itself attempts to transmit) and/or (D) the(corresponding) threshold may be adjusted according to the “CONGESTIONLEVEL”. When the V2X TX UE(s) selects (or reserves) SA TX-relatedresources, with respect to the SA transmission resource(s) associatedwith the data transmission(s) on the HARD_RSC and SOFT_RSC of other V2XTX UE(s) (determined from SA decoding), by applying a predefined (orsignaled) different “DM-RS POWER/ENERGY MEASUREMENT” threshold value (inthe same manner), the V2X TX UE(s) may be made to determine whether theHARD_RSC and SOFT_RSC are selectable (SA) candidate resources or (SA)resources to be excluded. Here, (A) the “TIME GAP” (range) between theSA transmission time and the associated data transmission time may beset (or signaled) differently according to in which resource type (forexample HARD_RSC and SOFT_RSC) the corresponding data is transmittedand/or (B) data related (transmission) power value (or (transmission)power control parameter) transmitted through a different resource type(and/or (maximum allowable) MSC value) may be set (or signaled)differently (or independently). In one example, the V2X messagetransmission period of the PEDESTRIAN UE (P-UE) (for example, “1000 ms”)may be set (or signaled) to be relatively long compared with that of aVEHICLE UE (V-UE) (for example, “100 ms”) (by taking into account therelatively low movement speed and/or a need for battery saving). Here,when the P-UE transmits a V2X message, the “I” value on the SA field ismade to indicate a predefined (or signaled) specific value (or “RESERVEDSTATE”) and therefore, other V2X RX UE(s) may be made to interpret that(A) the (corresponding) SA (and/or associated data) transmission hasbeen performed by the P-UE and/or (B) to interpret that the (scheduled)resource based on SA has been reserved with a predefined (or signaled)(different) period (relatively long (compared to the case of a V-UE).

[Proposed Rule#14] In one example, (A) if a plurality of (SIDELINK (SL))SPS PROCESS (or CONFIGURATION) (related to different services and/or V2XMESSAGE PRIROTY) is being operated at the same time (or beingactivated), the V2X TX UE(s) may be defined to exclude resources (wherea resource may be interpreted as a subframe in this case) related toother previously (or already) selected (SL) SPS PROCESS (orCONFIGURATION) from (selectable) candidate resources (STEP 2 of Table 2)when a specific (SL) SPS PROCESS (or CONFIGURATION) related transmissionresource is selected and/or (B) a predefined (or signaled)synchronization signal (PRIMARY SIDELINK SYNCHRONIZATION SIGNAL(PSSS)/SECONDARY SIDELINK SYNCHRONIZATION SIGNAL (SSSS)) (and/orPHYSICAL SIDELINK BROADCAST CHANNEL (PSBCH)) transmission (time (orfrequency)) resource (for example, “subframe”) may be defined to beexcluded from (selectable) candidate resources (STEP 2 of Table 2).

[Proposed Rule#15] In one example, if the V2X (TB) transmissionoperation is skipped at a specific time point according to a predefined(or signaled) “(DROPPING) PRIORITY” (for example, “WAN UL TX(s)” (and/orsynchronization signal transmission (resource)”) and the V2X (MESSAGE)TX(s) are overlapped (partly or completely) with each other in the time(or frequency) region), the resource reselection-related counter (Table2) value may be defined to be decreased blindly (and/or defined totrigger a resource reselection operation). In one example, if the“SYNCHRONIZTION SOURCE” of the V2X TX UE(s) is changed, the V2X TX UE(s)may be defined so that the resource reselection operation is triggered(and/or the resource reselection operation may be defined to betriggered only when a difference between the changed “SYNCHRONIZATIONSOURCE” related time (or frequency) synchronization value and theexisting “SYNCHRONIZATION SOURCE” related (time (or frequency)synchronization) value is larger than a predefined (or signaled)(maximum allowable) threshold value). In one example, if the“SYNCHRONIZATION SOURCE” of the V2X TX UE(s) is changed, the V2X TXUE(s) may be defined so that the transmission resource is selected (orreserved) randomly (when the remaining “LATENCY” value is less than apredefined (or signaled) threshold) (for example, a randomly selectedresource is defined to be used only for transmission of a predefined (orsignaled) number of “TRANSPORT BLOCKs (TBs)”, after which the “TB”transmission is performed through sensing-based selected (or reserved)resources) and/or (B) the transmission resource may be defined to beselected (or reserved) after a sensing operation is performed during apredefined (or signaled) (time) period. Here, in one example, the V2X TXUE(s) may be made to perform a sensing operation with respect to aplurality of (other) “SYNCHRONIZATION SOURCE” related communication(based on a predefined (or signaled) value) (including the current“SYNCHRONIZATION SOURCE”), and if one of the plurality of“SYNCHRONIZATION SOURCE” is changed, a transmission resource may beselected (or reserved) by using the corresponding (changed“SYNCHRONIZATION SOURCE″-related) sensing result.

[Proposed Rule#16] In one example, the V2X UE(s) may be defined toreport (independently) (A) capability of simultaneous reception (ortransmission) of a few of carriers synchronized with each other (in time(or frequency)) (or whose synchronization difference (in time (orfrequency)) is less than a predefined (or signaled)) threshold value)and/or to report capability of simultaneous reception (or transmission)of a few of carriers having different synchronization from each other(in time (or frequency)) (or synchronization difference (in time (orfrequency)) is larger than a predefined (or signaled) threshold value).In one example, a (serving) eNB which has received the (capability)information may take into account the capability of the (corresponding)V2X UE(s) and set (or signal) an appropriate number of carriers for thepurpose of V2X communication (reception (or transmission)). In oneexample, in the case of MODE 1 V2X communication, the (serving) eNB maysignal related information (to the V2X UE(s)) so that V2X TX operationmay be performed with a different MCS (range) value and/or a differentnumber of RESORUCE BLOCKs (RBs) and/or a different number of (HARQ)retransmissions according to the absolute speed of the V2X UE(s) and/or“SYNCHRONIZATION SOURCE TYPE (for example, GNSS and ENB)”. Here, in oneexample, the (serving) eNB may set (or signal) the “location-based poolsize” information differently according to the speed (or range) to theV2X UE(s) (within the coverage of the (serving) eNB) and make the V2XUE(s) perform V2X communication by applying (or using) the“location-based pool size” information corresponding to the speed of theV2X UE(s).

[Proposed Rule#17] In one example, (by taking into account (A) HARQCOMBINING operation with respect to reception of different REDUNDANCYVERSION (RV) (data) and/or (B) PSCCH payload size (increase) requiredfor (time) resource position information signaling related to data(re)transmission), the V2X TX UE(s) may make a plurality (NUM_RETX) ofspecific (one) TB-related data (re)transmission-related time resourcesselected within a predefined (or signaled) window (LIM_TIMEWIN). Here,if the corresponding rule is applied, the V2X TX UE(s) may be made toperform a sensing-based resource (re)selection operation according tothe (part of) the following method (for example, the STEP 2 or 3 ofTable 2). Here, the LIM_TIMEWIN value may be adjusted (or set (orsignaled) differently) according to (a) V2X MESSAGE PRIORITY that theV2X TX UE(s) attempts to transmit and/or (B) (measured) CONGESTION LEVELand/or (C) V2X MESSAGE (or SERVICE)-related TARGET LATENCY (orRELIABILITY) REQUIREMENT.

(Example#17-1) In one example, among (non-excluded) resources (NOEX_RSC)derived from performing the STEP 2 (of Table 2) (for example, OPTION2-1), if (specific TB-related) NUM_RETX data (re)transmission-relatedtime resources are not (all) selectable within the LIM_TIMEWIN (or thenumber of candidates that may be selected within the LIM_TIMEWIN is lessthan a predefined (or signaled) threshold), (A) (specific TB-related)NUM_RETX data (re)transmission is defined to be (all) skipped and/or (B)(specific TB-related) data (re)transmission is defined to be performed(partly) by using only (the maximum number of) time resources that maybe selected within the LIM_TIMEWIN and/or (C) (specific TB-related)NUM_RETX data (re)transmission-related time resources are defined to beselected (for example, if there is no selectable candidate within theFLIM_TIMEWIN, resource selection may be skipped) within an additionallypredefined (or signaled) window (FLIM_TIMEWIN) (to be used (or applied)to this particular case) (for example, “FLIM_TIMEWIN > LIM_TIMEWIN”)and/or (D) the PSSCH DM-RS RSRP THRESHOLD value (related to resourceexclusion) of STEP 2 (of Table 2) may be defined to be increased by apredefined (or signaled) offset value until (specific TB-related)NUM_RETX data (re)transmission-related time resources are (all) selectedwithin the LIM_TIMEWIN (or FLIM TIMEWIN) (or until the number ofcandidates that may be selected within LIM_TIMEWIN becomes larger than apredefined (or signaled) threshold). In one example, (after STEP 2 (ofTable 2) is performed (according to the rule)), when (specificTB-related) NUM_RETX data (re)transmission-related time resources areselected according to a predefined rule (for example, random selection)among resources of which the PSSCH DM-RS RSRP value in the lower (orupper) X % on the STEP 3 (of Table 2) has been measured, if (part of)selected time resources do not exist within the LIM TIMEWIN (orFLIMTIMEWIN), it may be defined so that (A) reselection is performed(until the corresponding condition is satisfied) and/or (B) (specificTB-related) NUMRETX data (re)transmission is (all) skipped and/or (C)(specific TB-related) data (re)transmission is performed (partly) byusing only the time resources located within the LIM_TIMEWIN (orFLIM_TIMEWIN).

[Proposed Rule#18] In one example, the PSCCH DM-RS related CYCLIC SHIFT(CS) (and/or OCC) value is fixed to a predefined (or signaled)(specific) value (for example, “CS INDEX = 0”, “OCC = [+1 +1]”). Here,if the corresponding rule is applied, and the PSCCH transmissionresources are (partly) overlapped between different V2X TX UE(s),PSCCH-related reception performance may not be guaranteed. Here, toalleviate the corresponding problem, the V2X TX UE(s) may be made toselect (one) CS (and/or OCC) value according to a predefined rule (forexample, random selection) within a predefined (or signaled) CS SET(and/or OCC SET). Here, the CS (INDEX) SET may be set (or signaled) to“CS INDEX 0, 3, 6, 9”. Here, the V2X RX UE(s) (since it does not knowexactly which value the V2X TX UE(s) has selected) performs blinddetection (BD) operation with respect to the (all) CS (and/or OCC)within the corresponding CS SET (and/or OCC SET). In one example, the CS(and/or OCC) value that the V2X TX UE(s) selects within the CS SET(and/or OCC SET) may be defined to be randomized (or hopped) by afunction (or equation) having an input parameter (or seed value) such as(A) (V2V) subframe (or slot) index and/or (B) V2X TX UE ID (or (TARGET)V2X RX UE ID) and/or (C) (X bit) ID transmitted on the PSCCH (and/or theCS SET (and/or OCC SET) (configuration) of the V2X TX UE(s) may bedefined to be randomized (or changed) by a function (or equation) havingan input parameter (or seed value) such as (D) (V2V) subframe (or slot)index and/or (E) V2X TX UE ID (or (TARGET) C2X RX UE ID) and/or (F) (Xbit) ID transmitted on the PSCCH. Here, the CS SET (and/or OCC SET)(configuration) may be set (or signaled) differently according to theV2X MESSAGE PRIORITY (that the V2X TX UE(s) attempts to transmit) and/or(measured) CONGESTION LEVEL. In one example, (if the aforementioned ruleis applied), to reduce the complexity related to (PSCCH DM-RS) CS(and/or OCC) BD operation of the V2X RX UE(s), the maximum number of BD(that the V2X RX UE(s) has to perform within one subframe) may be set(or signaled) (from a (serving) eNB). In one example, the V2X UE(s) maybe made to report the maximum number of BD that the V2X UE(s) mayperform within one subframe (to the (serving) eNB) through predefinedsignaling. In one example, the PSCCH SCRAMBLING SEQUENCE GENEATOR may beinitialized according to a (predefined (or signaled)) (all) CS (and/orOCC) values within the CS SET (and/or OCC SET) (and/or predefined (orsignaled) C_INIT value (for example, “510”)) selected by the V2X TXUE(s). (If the corresponding rule is applied) a CS field (for example,“3 bit”) may be defined on the PSCCH, and the corresponding CS fieldvalue may be designated (in the same manner) by (one) CS value(SELCS_VAL) selected according to a predefined rule (for example, randomselection) within the CS SET predefined (or signaled) by the V2X TXUE(s) (and/or by using a value derived (or calculated) by a predefined(randomization (or hopping)) function having an input parameter of theSELCS_VAL value), and according to the corresponding (designated) CSfield value, the PSSCH DM-RS CS value (associated with the PSCCH) may beset (or determined). Here, if the corresponding rule is applied, andinterference on the PSCCH DM-RS (CS) has been relieved (or randomized),the interference on the (associated) PSSCH DM-RS (CS) may be relieved(or randomized) (in the same manner). In one example, (if theaforementioned rule is applied), the PSSCH DM-RS value (associated withPSCCH) (instead of additionally defining a CS field (for example, “3bit”) on the PSCCH) may be set (in the same manner) by (one) PSCCH DM-RSCS value (SELCS_VAL) selected according to a predefined rule (forexample, random selection) within the CS SET predefined (or signaled) bythe V2X TX UE(s) (and/or by using a value derived (or calculated) by apredefined (randomization (or hopping)) function having an inputparameter of the SELCS_VAL value). Here, the PSCCH SCRAMBLING SEQUENCEGENEATOR may be initialized according to a CS field value (on the PSCCH)(and/or V2X TX UE ID (on the PSCCH) (or (TARGET) V2X RX UE ID (or ID ofX bits)) and/or (V2V) subframe (or slot) index).

In one example, when V2V communication is performed, PSCCH and/or(associated) PSSCH-related (A) (DM-RS) SEQUENCE GENERATION RULE and/or(B) (DM-RS) CS (or OCC) INDEX SELECTION (or DETERMNATION) RULE and/or(C) GROUP or SEQUENCE HOPPING RULE may be defined as shown in Table 7and 8. In one example, (part of) the following proposed methods describemethods for efficiently performing (DM-RS) SEQUENCE (or CS (or OCC)INDEX) (and/or interference) randomization operation when PSCCH and/orPSSCH transmission resources between different UEs are (partly orcompletely) overlapped with each other.

In what follows, with reference to Table 7 and 8, when V2V communicationis performed, examples of PSCCH and/or (associated) PSSCH-related (A)(DM-RS) SEQUENCE GENERATION RULE and/or (B) (DM-RS) CS(/OCC) INDEXSELECTION(/DETERMINATION) RULE and/or (C) GROUP/SEQUENCE HOPPING RULEare described. At this time, V2C WI support only normal CPs, and adestination ID may not be delivered through SA. Moreover, the 16 CRCbits from SA may be used for generating a PSSCH DMRS sequence and datascrambling sequence.

TABLE 7 Parameter PSCCH Group hopping disabled u 8 Sequence hoppingDisabled Cyclic shift n_(cs,λ) Chosen randomly out of {0, 3, 6, 9} by atransmitter, The chosen value is applied to a || DMRSs for SA within asubfra me Orthogonal sequence |w^(λ)(0) w^(λ)(1) w^(ℎ)(2) w^(λ)(3)| [+1+1 +1 +1| Reference signal length M_(sc)^(RS) M_(sc)^(PSCCH) Number oflayers υ 1 Number of antenna ports 1

Here,

r_(PSCCH)^((λ))(m ⋅ M_(sc)^(RS) + n) = w^((λ))(m)r_(u, v)^((α_(λ)))(n), m = 0, 1, 2, 3.

TABLE 8 Parameter PSSCH Group hopping enabled n_(X) n_(s)2n_(ss)^(PSSCH) + k, k = 0, 1 ƒ_(ss) [n_(x)/16]mod 30 Sequence hoppingdisabled Cyclic shift ^(n)cs.λ [n_(x)/2]mod8 Orthogonal sequence|w^(λ)(0) w^(λ)(1) w^(ℎ)(2) w^(λ)(3)| [+1 +1 +} +1}if n_(x)mod2=0 [+1 -1+1 -1]if n_(x)mod2=1 Reference signal length Number of layers ν 1 Numberof antenna ports P 1

Here,

r_(PSSCH)^((λ))(m ⋅ M_(sc)^(RS) + n) = w^((λ))(m)r_(u, v)^((α_(λ)))(n), m = 0, 1, 2, 3,

and n_(x) represents X bits in SA used for generating a PSSCH DMRSsequence.

[Proposed Rule#19] In one example, predefined (or signaled) (or randomlyselected) 2 bits may be scrambled with a selected PSCCH CS index (orvalue) (for example, “2 bit”) among bits (field) used for determining(associated) PSSCH DM-RS CS index (or value) (for example, 3 bits of“C₁₂, C₁₃, C₁₄” among 16 bit CRC of PSCCH (C₀, C₁, ... C₁₅)). In oneexample, when the aforementioned rule is applied, (A) the (final)16 bitCRC of the PSCCH may be kept (or applied) to the “C₀, C₁, ... C₁₅” value(for example, it is considered (or assumed) that only the CRC (and/orbit (field)) used for determining the (associated) PSSCH DM-RS CS index(or value) is changed by the (corresponding) SCRAMBLING operation and/or(B) a 16 bit CRC (part of) which has been changed due to the(corresponding) SCRAMBLING operation may become the (final) CRC of thePSCCH. In one example, 2 LSB (for example, when the corresponding ruleis applied, the PSSCH DM-RS OCC index (or value) may also be changed)(or MSB) bits (and/or predefined (or signaled) (or randomly selected) 2bits at specific positions) among the 16 bit CRC (C₀, C₁, ... C₁₅) ofthe PSCCH may be scrambled with the selected PSCCH CS index (or value)(for example, “2 bit”). In one example, when the aforementioned rule isapplied, (A) the 16 bit CRC (part of) which has been changed due to the(corresponding) scrambling operation may become the (final) CRC of thePSCCH and/or (B) the (final) 16 bit CRC of the PSCCH is kept (orapplied) to the “C₀, C₁, ... C₁₅” value (for example, it is considered(or assumed) that only the CRC (and/or bit (field)) used for determiningthe (associated) PSSCH DM-RS CS index (or value) is changed by the(corresponding) SCRAMBLING operation). In one example, (different) 16bits intended for scrambling are predefined (or signaled) for each PSCCHCS index (or value) (for example, “2 bit”), and the UE is made toscramble (A) the selected PSCCH CS index (or value) and associated 16bits meant for scrambling (S₀, S₁, ..., S₁₅) and (generated) 16 bit CRC(C₀, C₁, ... C₁₅) of the PSCCH, the (corresponding) scrambling result(W₀, W₁, ..., W₁₅) is made to become the final 16 bit CRC of the PSCCHand/or (B) the (final) 16 bit CRC of the PSCCH is kept (or applied) tothe “C₀, C₁, ... C₁₅” value, but only the 16 bit CRC (and/or bit(field)) used for determining the (associated) PSSCH DM-RS CS index (orvalue) may be used (or assumed) as the “W₀, W₁, , W₁₅” value (and/or 3bits of “W₁₂, W₁₃, W₁₄” from the “W₀, W₁, ..., W₁₅”).

In one example, (A) the SCI FORMAT configuration field(s) used for theMODE 2 V2V SCHEDULING (MODE2_SCH) operation and/or (B) the DCI FORMATconfiguration field(s) used for MODE 1 DYNAMIC V2V SCHEDULING(MODE1_DYN) operation may be defined as follows. In one example, in theFRA_INRETX field (similarly to the LVRB form of the existing LTEsystem), RESOURCE INDICATION VALUE (RIV) value may be defined to informof the (PSSCH transmission-related) (A) start sub-channel index (orposition) information (SUB_START) and/or length (or number) informationabout the sub-channel allocated (or positioned) continuously (in thefrequency domain) (SUB_LENGTH). In one example, when two times of PSSCHtransmission is set (or signaled) for specific (one) TB transmission,(A) the SUB_START value may be interpreted as the start index (orposition) information (SECDATA_SUBST) of a sub-channel in which thesecond PSSCH transmission is performed, and/or (B) the SUB LENGTH valuemay be interpreted as the sub-channel length (or number) information(SFDATA_SUBLN) used for the first and the second PSSCH transmission.Here, the start index (or position) information (FIRDATA_SUBST) of asub-channel in which the first PSSCH transmission is performed (insteadof being signaled directly through the FRA_INRETX field) may be made tobe figured out implicitly by the RX UE through (one-to-one) mapping (orlinkage) relationship between a predefined (or signaled) “((blindly)detected) (first) PSCCH resource index (or position) information” and“start index (or position) information of a sub-channel in which the(associated) (first) PSSCH transmission is performed”.

In what follows, examples of (A) the SCI FORMAT configuration field(s)used for MODE2_SCH operation and/or (B) the DCI FORMAT configurationfield(s) used for MODE1_DYN operation will be described.

SCI may include 1) PRIORITY: 3 bit, 2) resource reservation: 4 bit, 3)MCS: 5 bit, 4) CRC: 16 bit, 4) retransmission index (RETX_INDEX): 1 bit,6) time gap (TGAP_INIRETX) between transmission start andretransmission: 4 bit, 7) frequency resource position (FRA_INRETX) ofthe transmission start and retransmission: 8 bit, and 8) reserved bits(RSV_ BIT): 7 bit.

DCI may include 1) CIF: 3 bit, 2) minimum index of a sub-channelallocated for transmission start (PSCCH_RA): 5 bit, 3) time gap betweentransmission start and retransmission (as SA contents): 4 bit, and 4)frequency resource position (FRA_INRETX) of the transmission start andretransmission: 8 bit.

[Proposed Method#20] In one example, if one-time PSSCH transmission isset (or signaled) for specific (one) TB transmission, part of theinformation of (the aforementioned) FRAINRETX field becomes unnecessary(for example, “SECDATA_SUBST related information”). (In other words) inone example, the (only) information needed for the corresponding case issub-channel length (or number) information (FDATA_SUBLN) used for thefirst PSSCH transmission. Here, the (corresponding) unnecessaryinformation-related STATE (or value) and/or bits may be definedaccording to (part or all of) the following rules.

(Example#20-1) In one example, (A) when it is assumed that a maximum of20 sub-channels may be set (or signaled) as a (V2V) resource pool (onone subframe), the number of bits required to express FDATA_SUBLNinformation is “5” bit (namely “CEILING (LOG₂(20)) = 5” (here, as oneexample, CEILING (X) is a function which returns the least informationvalue greater than or equal to X)) and/or (B) when it is assumed that Ksub-channels are set (or signaled) as a (V2V) resource pool (on onesubframe), the number of bits required to express FDATA_SUBLNinformation becomes “CEILING (LOG₂(K))”.Here, in one example, when twotimes of PSSCH transmission is set (or signaled) for specific (one) TBtransmission, and the (required) FRA_INRETX field size is assumed to be“Q” bit (for example, “Q = 8”), the remaining bits of “(Q-5)” (and/or“(Q - CEILING (LOG₂(K))”) may be interpreted (or considered) asunnecessary information-related bits

(Example#20-2) In one example, if two times of PSSCH transmission is set(or signaled) for specific (one) TB transmission, and the (required)FRA_INRETX field size is assumed to be “Q” bit, a plurality of(predefined (or signaled)) (part or all of) SECDATA_SUBST value whichmay be designated together with an (actually needed) specific (one)FDATA­_SUBLN (or SFDATA_SUBLN) value may be interpreted (or considered)as unnecessary information-related STATE (or value).

(Example#20-3) if one-time PSSCH transmission is set (or signaled) forspecific (one) TB transmission, since the V2X RX UE(s) is capable ofdetermining whether the (corresponding) V2X TX UE performs one or twotimes of PSSCH transmission (with respect to a specific (one) TB)through the TGAP_INIRETX field, the RETX_ INDEX related STATE (or value)may be interpreted (or regarded) as unnecessary information. In anotherexample, if one-time PSSCH transmission is set (or signaled) forspecific (one) TB transmission, the RETX_INDEX related value (or STATE)may be designated by a predefined (or signaled) (specific) value (orSTATE). Here, in one example, (RETX_INDEX related) corresponding(specific) value (or STATE) may be used for “VIRTUAL CRC” applications.

(Example#20-4) In one example, part of predefined (or signaled) bitsamong the RSV_BIT field-related bits (for example, “7 bit”) may beinterpreted (or regarded) as the unnecessary information-related bits(or value).

In one example, according to (part of) the following rule, byrandomizing the (aforementioned) unnecessary information-related STATE(or value) and/or bit, the PSSCH (DM-RS) SEQUENCE (or CS (or OCC) INDEX)collision problem which occurs when PSSCH transmission resources ofdifferent UEs are (partly or completely) overlapped with each other maybe relieved (for example, (through the corresponding operation) thePSCCH CRC is randomized, and due to the randomization, (finally) thePSSCH (DM-RS) SEQUENCE (or CS (or OCC) INDEX) is randomized). In oneexample, the case in which the aforementioned unnecessaryinformation-related STATE (or value) and/or bit is occurred (forexample, the case where one-time PSSCH transmission is set (or signaled)for specific (one) TB transmission) is only an example, and (part or allof) the proposed method of the present invention may be extended to beapplied for various cases (in which unnecessary information-relatedSTATE (or value) and/or bit is occurred) (for example, (in the case ofMODE1_DYN_DCI_FORMAT and/or MODE2_SCH_SCI FORMAT), (additional) extrabits obtained as the FRA_INRETX size is changed according to the totalnumber of sub-channels (K) comprising a (predefined (or signaled)) V2Vresource pool (within one subframe) (for example, “(8 - CEILING (LOG₂(K·(K+1)/2)) (FRA_INRETX size))” (and/or “(8 - CEILING (LOG₂(K·(K+1)/2)) (FRA_INRETX size) -CEILING (LOG₂ (K)) (PSCCH­_RA size))”))(and/or with respect to a predefined (or signaled) (target) payload size(for example, the (target) payload sizes of the MODE1_DYN_FORMAT and theMODE2­_SCH­_SCI_FORMAT may become the (existing) DCIFORMAT 0 payload size(refer to the descriptions above) and 48 bit (refer to the descriptionsabove), respectively), (additional) extra bits generated as theFRA_INRETX size is changed may be regarded as the unnecessaryinformation-related bits). In one example, through the correspondingrandomization operation (of the unnecessary information-related STATE(or value) and/or bit), the 16-bit CRC of the PSCCH (C₀, C₁, ..., C₁₅)is randomized (or changed), and finally the PSSCH DM-RS CS (or SEQUENCEor OCC) (index) is also randomized (or changed) (refer to Table 7 and/orTable 8). Here, in one example, application of (part of) the followingrule to the (additional) extra bits generated as (A) (theaforementioned) (Example#20-3) and/or (B) (Example#20-4) and/or (C)FRA­_INRETX size are changed according to the total number ofsub-channels (K) comprising a (predefined (or signaled)) V2V resourcepool (within one subframe) may be limited to the case where the totalnumber of sub-channels comprising a V2V resource pool is set below apredefined (or signaled) value (for example, “I”) (which, for example,may be interpreted as a situation in which additional randomization ofPSSCH DMRS (or PSCCH CRC) is difficult to be derived (through thecorresponding field) as the FRA_INRETX field size is reduced (forexample, “0”)).

(Rule#20-1) In one example, the TX UE may set the (aforementioned)unnecessary information-related STATE (or value) and/or bit to arandomly selected value (and/or a predefined (or signaled) value by the(serving) eNB (or network)). Here, a condition for applying this rulefor each of the (aforementioned) unnecessary information-related STATE(or value) and/or bit (for example, (Example#20-1), (Example#20-2),(Example#20-3), (Example#20-4)) may be defined (or signaled)differently. Here, since the (actually used) FRA­_INRETX size becomes “0”when the number of sub-channels set (or signaled) as a resource pool(for V2X communication) is “1” (and/or when one-time PSSCH transmissionis set (or signaled) for specific (one) TB transmission), the rule isapplied to the unnecessary information-related STATE (or value) and/orbit of (Example#20-3) (for example, RETX_INDEX-related STATE (or value))and otherwise (for example, the case where the number of sub-channelsset (or signaled) as a resource pool (for V2X communication) is not “1”(and/or larger than “1”) (and/or the case where one-time PSSCHtransmission is set (or signaled) for specific (one) TB transmission)),the rule may be applied to the unnecessary information-related STATE (orvalue) and/or bit of ( Example#20-2) (for example, a plurality of(predefined (or signaled)) (part or all of) SECDATA_SUBST value (orSTATE) which may be designated together with (actually needed) specific(one) FDATA_SUBLN value). Here, in one example, (under a situation inwhich one-time PSSCH transmission is performed for specific (one) TBtransmission), irrespective of the number of sub-channels set (orsignaled) as a resource pool (for V2X communication), the rule is madeto be applied for the unnecessary information-related STATE (or value)and/or bit of (Example#20-3) (for example, RETX_INDEX related STATE (orvalue)), and only for the case in which the number of sub-channels set(or signaled) as a resource pool (for V2X communication) is not“1”(and/or larger than “1”), the rule may be applied to the unnecessaryinformation-related STATE (or value) and/or bit of (Example#20-2) (forexample, a plurality of (predefined (or signaled)) (part or all of)SECDATA­_SUBST value (or STATE) which may be designated together with(actually needed) specific (one) FDATA_SUBLN value).

(Rule#20-2) In one example, the TX UE may set the (aforementioned)unnecessary information-related STATE (or value) and/or bit to (A) TX(or (target) RX) UE ID and/or (B) the value derived (or calculated) by apredefined (randomization (or hopping)) function having a selected PSCCHCS index (or value) (for example, “2 bit”) as an input parameter or (C)TX (or (target) RX) UE ID and/or (D) a value derived from a selectedPSCCH CS index (or value) (for example, “2 bit”). In one example, if the(aforementioned) unnecessary information-related bit is defined in theform of (Example#20-1), and “(Q-5)” (and/or “(Q-CEILING(LOG₂)))”) (forexample, “Q = 8” and “K = 20”) is larger than the bit value (PC_SELSBIT)(for example, “2 bit”) representing the selected PSCCH CS index (orvalue), (A) among “(Q-5)” (and/or “(Q-CEILING(LOG₂(K)))”) bits, (bit)positions which have to be designated for the PC_SELCSBIT bit (or value)(or bit (or value) derived as the PC_SELCSBIT bit) are set (or signaled)and/or (B) the remaining bits (for example, “1” bit) of“(Q-5-PC_SELCSBIT)” (and/or “(Q-CEILING(LOG₂(K)) ­- PC_SELCSBIT)”) may bepadded with zeros (or set to a predefined (or signaled) specific value).

In one example, if one-time PSSCH transmission is set (or signaled) forspecific (one) TB transmission, the (aforementioned) FRA_INRETX fieldsize may be reduced (exceptionally) (for example, “(Q-5)”,“(Q-CEILING(LOG₂(K)))”).

In one example, (if the PSSCH (associated with PSCCH) is transmitted inthe form of “FDM”), the PSCCH CRC used for determining parameters suchas (DM-RS) SEQUENCE (or CS (or OCC) INDEX) related to the PSSCHtransmitted at a specific time point may be defined as the PSCCH CRCtransmitted at the same time point with the PSSCH (and/or PSCCH CRCtransmitted (always) together for PSSCH transmission).

Since examples of the proposed methods described above may also beincluded as implementation methods of the present invention, it isapparent that the examples may also be regarded as a kind of proposedmethods. Also, although the proposed methods above may be implementedindependently, they may be implemented in the form of a combination (ormerge) of part of the proposed methods. In one example, although thepresent invention describes the proposed methods on the basis of the3GPP LTE system for the convenience of descriptions, the range ofsystems to which the proposed methods are applied may be expanded toinclude other systems in addition to the 3GPP LTE system. As oneexample, the proposed methods of the present invention may be extendedto be applied for D2D communication. Here, in one example, D2Dcommunication refers to communication performed by a UE directly toother UE using a radio channel, where in this example, the UE means aterminal of the user; however, when a network device such as an eNBtransmits or receives a signal to and from a UE according to acommunication method, the eNB may also be regarded as a kind of UE.Also, as one example, the proposed methods of the present invention maybe applied limitedly only to the MODE 2 V2X operation (and/or MODE 1 V2Xoperation). Also, in one example, the proposed methods of the presentinvention may be applied limitedly only for a case where the‘(transmission) resource (re)selection operation’ is triggered(according as a (predefined (or signaled)) condition is satisfied), anda (generated) packet (or message) (to be transmitted) exists on the‘(LOW LAYER) buffer’ (and/or ‘PDCP LAYER’) (or when a packet (ormessage) is generated) (and/or when a (generated) packet (or message)(to be transmitted) does not exist on the ‘(LOW LAYER) buffer’ (and/or‘PDCP LAYER’) (or when a packet (or message) is not generated)). Also,in one example, the proposed methods of the present invention may beapplied limitedly only for a case where the PSSCH (associated with thePSCCH) is not positioned (or positioned) at the neighboring RS(s) on thesame subframe. Also, in one example, the proposed methods of the presentinvention may be extended to be applied not only for the V2V MODE 1 (orMODE 2) DYNAMIC SCHEDULING operation but also V2C MODE 1 (or MODE 2)SEMI-PERSISTENT SCHEDULING (SPS) operation (and/or V2X MODE 1 (or MODE2) DYNAMIC SCHEDULING operation and/or V2X MODE 1 (or MODE 2) SPSoperation). Also, in one example, “transmission resource selection” inthe present invention may be (extended to be) interpreted as“transmission resource (re)reservation”.

FIG. 39 is a block diagram of a UE in which an embodiment of the presentinvention is implemented.

Referring to FIG. 39 , the UE 1100 comprises a processor 1110, a memory1120, and a Radio Frequency (RF) unit 1130.

According to one embodiment, the processor 1110 may embody the function,operation, or method of the present invention. For example, theprocessor 1110, performing sensing during a UE-specific sensing period,may select a resource with which to perform V2X communication andperform V2X communication on the basis of the selected resource.

For example, the processor 1110 may select a resource with which toperform V2X communication within a range satisfying the latencyrequirement and perform V2X communication on the basis of the selectedresource.

For example, the processor 1110 may perform sensing in units ofsub-channels having the size corresponding to the size of a sub-channelused for V2X message transmission, select a resource with which toperform the V2X message transmission, and perform V2X messagetransmission on the basis of the selected resource.

For example, the processor 1110 may perform reservation of a finitenumber of resources with which V2X communication is performed andperform the V2X communication on the finite number of resources.

For example, the processor 1110 determines whether a resourcereselection condition is satisfied, and if the resource reselectioncondition is satisfied, performs reselection of a resource with whichV2X (Vehicle-to-X) communication is performed, and perform the V2Xcommunication on the basis of the selected resource.

For example, the processor 1110 may select a subframe excludingsubframes related to the subframe in which transmission is performedduring a sensing period from a sensing window and perform V2Xcommunication on the basis of the selected subframe.

For example, the processor 1110 may allocate a V2X resource pool withrespect to the remaining subframes except for a specific subframe andperform V2X communication on the allocated V2X resource pool.

The RF unit 1130, being connected to the processor 1110, transmits andreceives a radio signal.

The processor may include Application-Specific Integrated Circuit(ASIC), other chipsets, logical circuit and/or data processing device.The memory may include Read-Only Memory (ROM), Random Access Memory(RAM), flash memory, memory card, storage medium and/or other storagedevice. The RF unit may include a baseband circuit to process a radiosignal. When embodiments are implemented by software, the methodsdescribed above may be implemented by a module (process, function, andso on) which performs the functions described above. A module may bestored in the memory and executed by the processor. The memory may beinstalled inside or outside the processor and may be connected to theprocessor via various well-known means.

What is claimed is:
 1. A method of performing a sidelink operation in awireless communication system, the method performed by a user equipment(UE) and comprising: determining a sidelink resource set based on acandidate resource set and a candidate resource, wherein the candidateresource is excluded from the candidate resource set, wherein a timeunit index of the candidate resource is determined based on a time unitindex of a specific time unit in which the sidelink operation isperformed within a sensing window of the UE; and performing the sidelinkoperation based on the sidelink resource set, wherein the time unitindex of the candidate resource is Y, wherein the time unit index of thespecific time unit is M, wherein the candidate resource is determinedbased on Y and M satisfying a condition that: Y+J*P = M+I , wherein ^(∗)represents multiplication, wherein the J is at least one integer valueof from 0 to a Cresel-1, wherein the Cresel is a positive integerrelated to a resource reselection counter, wherein the P is a valuerelated to a first resource reservation interval, and wherein the I is avalue related to a second resource reservation interval.
 2. The methodof claim 1, wherein the candidate resource is on a time unit within aselection window in which the UE selects at least one sidelink resource.3. The method of claim 2, wherein the selection window has a duration of100 ms.
 4. The method of claim 1, wherein the Cresel is proportional toa value of the resource reselection counter, which is randomlydetermined by the UE.
 5. The method of claim 4, wherein the value of theresource reselection counter is greater than or equal to 5 and less thanor equal to
 15. 6. The method of claim 1, wherein the sensing window hasa duration of 1 s.
 7. The method of claim 1, wherein the sensing windowis specific to the UE.
 8. The method of claim 1, wherein the firstresource reservation interval is provided based on a higher layer.
 9. AUser Equipment (UE) configured to perform a sidelink operation in awireless communication system, the UE comprising: a transceiver; atleast one processor; and at least one computer memory operablyconnectable to the at least one processor and storing instructions that,when executed by the at least one processor, perform operationscomprising: determining a sidelink resource set based on a candidateresource set and a candidate resource, wherein the candidate resource isexcluded from the candidate resource set, wherein a time unit index ofthe candidate resource is determined based on a time unit index of aspecific time unit in which the sidelink operation is performed within asensing window of the UE, and performing the sidelink operation based onthe sidelink resource set, wherein the time unit index of the candidateresource is Y, wherein the time unit index of the specific time unit isM, wherein the candidate resource is determined based on Y and Msatisfying a condition that: Y+J*P = M+N*I , wherein ^(∗) representsmultiplication, wherein the J is at least one integer value of from 0 toa Cresel-1, wherein the Cresel is a positive integer related to aresource reselection counter, wherein the P is a value related to afirst resource reservation interval, and wherein the I is a valuerelated to a second resource reservation interval.
 10. An apparatusconfigured to control a User Equipment (UE) to perform a sidelinkoperation in a wireless communication system, the apparatus comprising:at least one processor; and at least one computer memory operablyconnectable to the at least one processor and storing instructions that,when executed by the at least one processor, perform operationscomprising: determining a sidelink resource set based on a candidateresource set and a candidate resource, wherein the candidate resource isexcluded from the candidate resource set, wherein a time unit index ofthe candidate resource is determined based on a time unit index of aspecific time unit in which the sidelink operation is performed within asensing window of the UE; and performing the sidelink operation based onthe sidelink resource set, wherein the time unit index of the candidateresource is Y, wherein the time unit index of the specific time unit isM, wherein the candidate resource is determined based on Y and Msatisfying a condition that: Y+J*P = M+N*I , wherein ^(∗) representsmultiplication, wherein the J is at least one integer value of from 0 toa Cresel-1, wherein the Cresel is a positive integer related to aresource reselection counter, wherein the P is a value related to afirst resource reservation interval, and wherein the I is a valuerelated to a second resource reservation interval.